Bookmarks package: auto-detect source files encoding

[polyvertex]

For now, every plugin of the Bookmarks package assume the files they open are encoded in utf-8. Unfortunately the file formats used by Chrome, Firefox and others may evolve and Bookmarks plugins should be more flexible for that matter.

If you have an output that looks like the following in your console, this issue is for you:

WARNING: Bookmarks.Bookmarks: Failed to read Firefox's profiles file "C:\Users\you\AppData\Roaming\Mozilla\Firefox\profiles.ini". Error: File contains no section headers.
file: 'C:\Users\nero\AppData\Roaming\Mozilla\Firefox\profiles.ini',
line: 1
'\udcff\udcfe[\x00G\x00e\x00n\x00e\x00r\x00a\x00l\x00]\x00\n'