Not so small input.js (originally been batch training) cleanup
- Move selection_panels.js helper functions into a separate file
- Move unit_action helper functions from input.js into unit_actions.js
- Rearrange some functions, to better represent the execution flow
- Make batch training use g_NumberOfBatches instead of g_BatchTrainingCount so remember the number of batches instead of the number of units to train (needed for finishing P60)
- Simplify the batch training code a bit
- Also cleanup the moved functions a bit
Reviewed by: bb, Commented by elexis
Differential Revision: https://code.wildfiregames.com/D753