Add initial cross platform key mapping

[daniel-dressler]

Requires a version of native with support for key pass through. Use this version of native if ector has not merged my pull request yet: https://github.com/daniel-dressler/native

This pull request adds key mapping support for SDL and maybe Android if the build passes. It provides a new key mapping screen within the settings. It does not tackle analog sticks at present. I am thinking about how best to support analogs but nothing sounds good yet.

Other platforms will be broken if they do not define LEGACY_KEY_MAPPING
See UI/EmuScreen.cpp for where this define is used.

Since this request adds a couple new files and headers could I ask other platform users to test building? If possible I would appreciate pull requests if you can get the other platforms building with these changes. I do not suggest ector merge this request until the other platforms have defined LEGACY_KEY_MAPPING and fixed any build errors.

[daniel-dressler]

I have not merged with mainline in a few days so you may have to clone my repo into a new folder for testing.

[adriandennis17]

I will be testing this out.

Also touch screen analog.. is what i would use. trying to keymap an analog stick, dont think that would work well...

[daniel-dressler]

Thank you for mentioning the touch screen inputs, I may have broken those. After work I will take a look.

[adriandennis17]

Also we need an option, to show the on-screen analog " only " if were gonna use QWERTY keyboard we don't need the on-screen controls to be shown, just the analog,

Also if we untick on-screen controls from the control settings , its not disable its only hidden, and if you should touch somewhere on the screen you can still move around etc...

I think two settings can be implemented:

1. To disable on-screen touch control.
2. To hide the on-screen touch control

[daniel-dressler]

@hrydgard this should be ready for commit. It should merge clean.

Non-sdl platforms should work by default. SDL itself has the key mapping working.

@adriandennis17 I think those issues are out of my scope. I theory I should get key mapping to the analog stick working. In practice it may take me a few weeks to find a solution I like.

[adriandennis17]

Ok cool, .....

[hrydgard]

I don't like how it says "ERROR: Key already used" without saying where it's used, apart from that, it's okay. Merging.

[adriandennis17]

Cant wait to test this out.... this feature should have been

implemented with the first release of v0.8

Device: Droid 3

[daniel-dressler]

This gist should help with supporting modern key input for other platforms: https://gist.github.com/daniel-dressler/5924481