Monitor .desktop files added to ~/Desktop

It is possible to add web pages and apps to the desktop, but
chrome just adds a .desktop file to ~/Desktop which nothing
will see. So monitor for .desktop files created there and
do what is necessary for them to appear on the desktop.

Change-Id: Id21ad84e2d67e5a75d70727470cd164d89d3b850
Signed-off-by: Emilio Pozuelo Monfort <emilio.pozuelo@collabora.co.uk>
Set the right StartupWMClass in .desktop files

The application WM_CLASS' instance is not
"chrome.google.com__webstore_category_home", but the application
id (prefixed by "crx_"). Thus set StartupWMClass to that so that
GNOME Shell can properly match the application window to its
desktop file.

This is what Chrome sets StartupWMClass if you create the .desktop
file through "Create Shortcuts..." in the app's context menu.

Change-Id: I5d398b54037db9ee2c2d735f0fcd2026e0611ead
Signed-off-by: Emilio Pozuelo Monfort <emilio.pozuelo@collabora.co.uk>
Don't pass --app to Chrome

It's not necessary as we pass --app-id, and --app overrides
WM_CLASS, which prevents GNOME Shell from matching the app
to the right .desktop file.

This follows Chrome's .desktop files which pass --app-id but
not --app.
Fix Exec path in Chrome 28's .desktop files

Chrome 28 creates .desktop files with a broken Exec line,
which makes them completely useless.

Also remove workaround for missing newline character, it
has been fixed upstream and we no longer need it, see
https://code.google.com/p/chromium/issues/detail?id=169660

Change-Id: I4155c641dd3b10b334fd713704e53f86853a417e
Signed-off-by: Emilio Pozuelo Monfort <emilio.pozuelo@collabora.co.uk>
Bug: https://code.google.com/p/chromium/issues/detail?id=247574