Fixes several aero and dark shell issues

Fixes:
* https://github.com/adobe/brackets/issues/7222
* https://github.com/adobe/brackets/issues/5288
* https://github.com/adobe/brackets/issues/6801

Two issues reported by @MartinMa 

Adds:
* cef_buffered_dc class for easier implementation of buffered drawing whenever needed
* inactive border drawing state