Allow opening any directory from kate as project

This allows you to open any directory as project in Kate. Currently only kate /path/ will work, but a menu entry "Open folder..." can be added as well. A project for a directory is created if and only if a user explicitly asks for it i.e., kate . will load the current directory as a project, however kate will not and neither will kate somefile.txt. This is intentional so that we don't end up creating projects everytime someone opens a file or launches kate. In addition to that, there's a new action under Projects->Open Folder... which will open the selected directory as project in Kate.

Signed-off-by: Waqar Ahmed waqar.17a@gmail.com