Add offline functionality

[hrehfeld]

• disable installing,
• show message,
• use old xml.

[SpiritQuaddicted]

don't disable installing if repositoryBase is set to a local path

• add screenshotBase or something so one can use local screenshots too

[SpiritQuaddicted]

This is for me, so I don't forget:

"src="file://localhost/home/blah/path/reviews/screenshots/"

defaults.setProperty("repositoryBase", "file://localhost/blah/path/filebase/");