Quick open improvements

- Allow opening a file at a specifc line:col. This will happen if you
add a ':' at the end and specify line and column. For example:

"kaapp.cpp:201:18"

will open a file the selected file in tree at line 201 and column 18 (if
they exist).
- On clearing filter text, try to restore the sorting i.e., bring opened
documents at the top again.

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