Improved FileDialog Side-Panel + OS compatibility

[Bamboy]

This PR improves the FileDialog class:

Restructured the way "place" and "drive" directories are queried from the system, to be OS independent:

• On Linux, drives are queried from the system using bash lsblk command.
• Mac is still using the old (windows) way of "places/drives" - I did not add Mac/OSX support.
• "Places" under the user's HOME folder are now adjustable per-OS. (Not configurable)
• Added user Documents, Pictures directories.
• Added support to override the "places/drives" widget-list creation at a few different points.

Crashing will still occur if you navigate to a directory the app doesn't have permissions for.
This is untested on anything other than my Linux system.

[Bamboy]

Above image with changes, from my linux system (MyraPad)

Some notes:

• INITDISK R5 is a USB stick. Others are internal hard drive partitions.
• sdc2 is my main OS filesystem mounted at /home. It has no LABEL on the system, hence why no name in the UI.
• [Home] bamboy directs to /home/bamboy - I thought this looked better next to the other display elements. (The behavior I worked around would have been displaying as /home/bamboy)
  ...
• Changed [Brackets] instead of (Parenthesis) around VolumeLabel, applies all OS. Understandable if this is undesirable.

[rds1983]

thanks!