Rename all -panel icons to -symbolic

[Jeremy Bícha]

The Ubuntu mono themes use a -panel suffix for icons. The standard convention as used by the reference Adwaita/GNOME theme is use a -symbolic suffix.

Here's a partial list of icons to demonstrate.
/usr/share/icons/HighContrast/scalable/status/user-idle.svg
/usr/share/icons/Humanity/status/24/user-idle-panel.svg
/usr/share/icons/Humanity/status/24/user-idle.svg
/usr/share/icons/Humanity-Dark/status/24/user-idle-panel.svg
/usr/share/icons/gnome/24x24/status/user-idle.png
/usr/share/icons/gnome/scalable/status/user-idle-symbolic.svg
/usr/share/icons/ubuntu-mono-light/status/24/user-idle-panel.svg

Because of this bug, using the Adwaita theme with Unity looks bad because it falls back to using full-color icons since GNOME doesn't ship any -panel icons. This also breaks any other theme that was designed for GNOME3 without taking into account the Ubuntu special case.

This will need some coordination as not all ubuntu-mono icons ship a fallback icon. For instance, there's a battery-good-charging-symbolic.svg but not a battery-good-charging.svg. Without a fallback icon, the indicators will be "invisible" as they won't have an icon to show until the indicators are updated to try to load -symbolic icons.

Test Case
1. Install gnome-themes-standard
2. Open System Settings. In the Appearance panel, change the theme to Adwaita
3. The indicator icons should change slightly but still be symbolic/monochrome.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: ubuntu-mono 0.0.49
ProcVersionSignature: Ubuntu 3.5.0-17.28-generic 3.5.5
Uname: Linux 3.5.0-17-generic x86_64
ApportVersion: 2.6.1-0ubuntu6
Architecture: amd64
Date: Sun Nov 4 14:41:50 2012
MarkForUpload: True
PackageArchitecture: all
SourcePackage: ubuntu-mono
UpgradeStatus: No upgrade log present (probably fresh install)