(POC) Large effect count management

[willmmiles]

Pursuant to the ongoing discussions regarding handling large numbers of effects, this spike targets the core API changes I think set the most practical direction for future effect management. The design intent is to preserve compatibility with existing APIs (up to the 255 effect limit), and open a way for new APIs to break that limitation with minimal disruption to existing integrations.

First, the internal upgrade:

The key API changes center around supporting "non-contiguous" effect IDs -- be it names, a paging system, a usermod indexing scheme, or whatever. In all cases, the "effect identifier" is no longer strictly an index in to a vector. To this end, I refactored the effect metadata to a new struct Effect, keeping all per-effect information (name, function, id) in one place, and built an interface that relies on using functions to look up the Effect entry by name or ID.

Internal API changes:

• New:
  • Adds new struct Effect to collect effect-related data in one place
  • Moves global list of effects from class WS2812FX to new namespace Effects
  • Add effect lookup functions Effects::getEffectById() or Effects::getEffectByName(). Function implementations can be replaced or extended to support different indexing approaches (larger id type? numeric ID maps?) without breaking API compatibility.
• Changed:
  • Segments now use an Effect* to look up the function.
  • Mode-related API on WS2812FX now implemented by calling Effects namespace functions.
  • Segment::mode is preserved for API compatibility, but marked as deprecated.
• Removed:
  • WS2812FX::getModeDataSrc() was the one existing internal API that could not be trivially supported. This impacted one usermod.

External API changes:
None. (Or at least none intentionally; I might have missed a special case re "Solid"'s metadata (or lack thereof)). Endpoints 'json/fxda' and 'json/eff' continue to return arrays where the index in to the array matches the 'getEffectById()' callback. Those arrays remain limited to 255 entries to ensure strict compatibility.

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From there, the external JSON API is expanded:

• New 'json/fxmap' endpoint returns a JSON object, where keys are the effect names, and the values objects of the form {"info": "...", "id": id}, where "id" is only present if the effect id is representable in a uint8_t. This allows an arbitrarily long list of effects to be described to a client without gaps for unused IDs.
• JSON API now accepts {"ef": "effect name"} when deserializing a segment, and emits this key when serializing. If "ef" and "fx" are both supplied, "ef" has precedence.

The following commit adapts the web UI to use this API instead of ids.

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The last commit saves some RAM by moving the Effect objects to code space.

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Implementation notes:

• I have made no effort to optimize effect name/id lookup. This does not matter to rendering as the Effect pointer is stored directly. This could be added later to speed up some of the API calls.
• A strnchr_P function for ESP8266 would be nice.
  • or alternately, we could choose to store effect name and metadata in separate literals. That might be a breaking API change though - I don't know if it's possible to constexpr-transform the existing literals at compile time.
  • Another alternative might be store the name length (calculated at compile time).
• Automatic "legacy" ID assignment is still performed for effects up to 255. After that either names will still work; and the architecture permits us to easily expand the numeric ID data type and/or add some expanded ID space as a new API (pages, a configurable mapper, or all of the above).
• Functions to select a random effect, or "step through" effects, could be added to namespace Effects. Current implementations of these features in various endpoints work by mutating IDs, which will be problematic if the ID space becomes sparse.
• The fxmap endpoint implementation either fits a whole effect in to a packet, or defers it for the next one. This is an inefficient use of bandwidth: keeping a local line buffer would allow it to be more bandwidth friendly at the cost of more RAM usage.
• This implemention still keeps all Effect*s in a dynamically allocated vector. A future design could also offer a compile-time static list, saving a bit more RAM. The dynamic list could be kept (it's cost is small when empty) for compatibility with older APIs as well as providing a foundation to support runtime-defined effects (ARTI-FX or similar) as fully integrated members.

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