Update vimrc & gitignore_global

 - Testrun Pt instead of Ag
 - Select different tab listchar
 - Fix .DS_Store ignore
 - Add .ackrc to ignores as it's usually placed per project
 - Have UTF-8 explicitly set as .vimrc source encoding
 - Minor reordering & refactorings

Signed-off-by: Aleksandrs Ļedovskis <aleksandrs@ledovskis.lv>