Add dependencies when used as a plugin to configuration file.

Define the various dependencies and information when the
client is used a a plugin.
Move user notification to main class.
Remove whitespace in dependencies list.
Handle the fact that the tag can have not child nodes.
Add support for and/or when checking dependencies list.
Adjust warning message depending on the conjunction used.
Indicate when dependencies are used.
Ignore dependencies if used as Fiji plugin.
Merge pull request #558 from jburel/plugin-dependencies

Plugin dependencies