New Frontpage content area

Adds a new box where custom content can be entered
Updating Readme

Updating readme with new features for version 2.5.4
Bumping version Number
Updating readme with Moodle version requirement
Updating translation
Merge branch 'MOODLE_254'
Updates to German translation
Merge branch 'MOODLE_254'
toggle block display on gradebook
Removing old code