The goal is to avoid confusion described in issue #6422 by removing
duplicates between the Theme and owncloudTheme.
- Use the about from ownCloudTheme everywhere
- Create default applicationIcons() and condifFileName() that should work
everywhere
- trayFolderIcon was removed as it is not used
- the helpUrl from the default Theme now points to the owncloud client
documentation. Before there was no help entry by default for branded
client if the function was not overriden.
- Do not merge functions that would otherwise break compatibility with
theme that did not override them. For example colors or customMedia.
