User interface
--------------
 - Make links clickable (about dialog)
 - Underline labels that have tooltips
 - Implant viewer
 - Fix caching to detect error documents
 - Create .bak files before cache files are overwritten
 - Reload skill in training after training finishes


Skill Browser / Planner
-----------------------
 - Add "Skill Group" column?
 - Priorities?
 - Move multiple skills at once!

 - Optional:
   - Subplan
   - Enabled skills through training


Remove SkillInTraining.xml
--------------------------
 - Requires to update a lot of stuff

   - Update GtkCharSheet
     - Change training_fetcher to skillqueue fetcher
     - Change trainsheet_info_label to skillqueue_info_label
     - Change training (sheet) to skillqueue

   - Update GuiSkillPlanner
     - Simply forward the queue sheet instead of training sheet

   - Update GtkTrainingPlan
     - GtkSkillList
       - Requires valid, in_training
       - Requires skill_id, to_level, end_time
       - Update GtkSkillIcon or add "bool inqueue"
     - GtkTraininPlan
       - Simply forwards the sheet
       - Update icons

   - Update notifier
     - It simiply requires skill_id and to_level

   - Update Skill Queue GUI
     - Sheets needs to be passed
     - Pay attention to training times


Notifications
-------------
 - Notification a few miniutes before actual finish


Skill / Certificate Browser
---------------------------
 - History: Check if element is in history, move to the end of history
