add classic left-click orders
improve the classic mouse behaivor

- don't require to deselect units to change selection
- fix issue with broken building placement on right-click orders
- don't select enemy units when left-click attacking
- build palette won't interfere with unit orders anymore
let Chronotank/Minelayer accept left-click-orders
pull mouse button preference from global property
Asynchronous loading of map previews in the map chooser dialog
Fixed the asynchronous map loading behavior when changing filter
fix make for mono 3

error CS1902: Invalid debug option `+'.
Valid options are `full' or `pdbonly'
Update CHANGELOG

Just a couple things added