[bug] Removed assumptions regarding the path of the plugin

There where errors occuring when the plugins path was not
'wp-content/plugins/eexcess'. That was due to the hardcoding of the
'eexcess'-part. This has was substituted with a dynamic path.
[feature] Citations are now immutable

The immutability of citations is the foundation for the "edit
citations"-feature, that allows the user, in a seprate dialog, to edit
the citations
[feature] remove function for citations implemented

There is now a new feature that allows the user to remove citations.
it's half-backed right now, but improvements will follow.