Fix responsiveness of RGA GUI disassembly view

The GUI becomes unresponsive for several seconds whenever the disassembly view gains or loses focus due to the code unnecessarily applying a stylesheet to the entire frame just to change border color, which seems to be a leftover functionality, considering that the color was only affected by the API used which is now chosen at application launch so the border color does not provide much value. According to the Qt documentation applications should not call setStylesheet() outside of the constructor because it's very costly and the current code calls it on focus change.

This change fixes that by getting rid of all the code using setStylesheet() to change the disassembly view's border.

Also, some missing header includes were added which most likely were uncovered by compiling against Qt 5.11.2 contrarily to Qt 5.9.2 recommended in the RGA documentation.

Note: the reason the entire rgIsaDisassemblyView.cpp is marked as changed is because it contained inconsistent line endings previously.