Modernise IsStartNode()

[originalfoo]

Replaces obsolete ExtSegmentManager.IsStartNode() with NetSegment extensions - either IsStartnode() IsStartNode() (always returns a bool) or IsStartNode() GetRelationToNode() (may return null if node not attached to segment) as applicable.

Additionally, updates a few encountered for loops like for (int i = 0; i < 8; ++i) to more descriptive for (int segmentIndex = 0; segmentIndex < Constants.MAX_SEGMENTS_OF_NODE; ++segmentIndex).

Small number of other minor tweaks - eg. to replace some other obsolete stuff in proximity/relation to the main task.

Probably has a lot of overlap with stalled PR #1272.

[kianzarrin]

we also have IsstartNode() that does returns a simple bool.

[originalfoo]

we also have IsstartNode() that does returns a simple bool.

I assume you mean IsStartnode() (lowercase n) ? I'm already using that one where simple bool is required (it's slightly faster as it only does one comparison).

I couldn't find any IsstartNode() method with the lowercase s.

[kvakvs]

And then I kinda like this code change

[originalfoo]

bump :)

[krzychu124]

Looks good, didn't notice problems