Fixed url filtering.

    The removing of commented-out or empty line is now no
    longer done by manipulating the array we iterate over.
    (Which is generally a bad idea)
Merge pull request #32 from NiklasMM/fix/filter_url_list

Fixed url filtering.
First early version of management app
App can now read feeds file and put the data into the table.
Added checkboxes to hide feed.

    Hidden feeds will remain in the feed list, but won't be displayed in the applet
Added function to read the entries from the table
Added functionality to remove entries.
Added add_feed button and fixed issue with delete.
Added listeners to url and title change.
Added checkbox functionality.
Feed file is now written upon save.
Remove use of feeds file and convert url setting to multi-line

- Remove use of feeds file from settings
- Use the same format for multi-line feeds as the feed file used
- Make the url setting bidirectional so the applet can update it
- Provide a migration function to auto-update feeds url lists in the
  legacy "space-separated" style to the "newline-separated" style
Start port of feed management app to GTK
Basic GTK management applet functional

- Added buttons
- Fixed-up add/remove/save code
- Change "Disabled/Hidden" column to "Enable" toggle
- Added window icon
Fix window icon path
Management app can read/write feed data from stdin/stdout

- Use stdin/stdout when no filename specified
- Can still use a file by passing the filename as the first argument
Move management app path
Launch feed managment app from applet

- Added to context menu
- Run management applet in async mode (otherwise we block the whole
  Cinnamon process!) and read the stdout to get new feeds
- Update applet settings with the output of the management applet
Store Feed URLs in hidden applet setting

- A "textview" setting would be preferred, but this is only available in
  Cinnamon >= 2.0.x. Dropping support for Cinnamon 1.8.x is not an
  option yet. For now we will only support managment of feeds via the
  management app
- Add button to settings to launch management app
Remove conversion from legacy url list

- This function does not work in practice since the type of the "url"
  setting has changed, which causes Cinnamon to reset it to the default
  value on upgrade (see _do_upgrade in
  /usr/share/cinnamon/js/ui/settings.js)