McHorse's McLib

This is a patch update which reworks file tree system, improves texture picker GUI and a couple of other neat features.

• Added key repeating (Keyboard.enableRepeatEvents(true);) (suggested by Tschipp)
• Added "Open folder" to texture picker to open current folder
• Added Interpolations.envelope() methods which allow to easily make fade in/out factor calculations based on given time value, and durations of fade in, sustain and fade out
• Added background option for list elemenet
• Added refreshing of current folder in texture picker
• Added IResourceTransformer to allow fixing any resource locations created via RLUtils
• Added keyboard control to texture picker. You can now use arrows up/down to go up and down in the list, shift + arrow up/down to jump in the beginning/end of the list, type in the name to select the closest matching and enter to select the file/enter the folder
• Changed the way file tree system works to allow lazy loading (instead of full tree generation) and check for changes