Release 0.5.1

Bugfix and minor improvements release. Still a long way to go but it keeps getting better :)
A lot of improvements concerning the marketplace feature (which is active again with this release). Still needs more testing though...
Also important to note that some work concerning the MySQL db support has been done (thx @aabeling !). SonarQuest should now be working with MySQL (also needs more testing, ofc).

Other work that has been done includes:

• Some buttons in the gm area are now only active if they can actually be used (instead of allowing dialogues to open that cannot be finished)
• Feature: admin can now see all worlds which the developers have joined
• Fixed issue #150
• Fix: no table headers when no world is active (admin/gm/dev area)
• Various translation fixes w/ artefacts and skills
• Fixed translation when world is not selected (top left)
• Fix: disable issue retrieval from server when no world is active
• Bugfix: user passwords were broken when the admin edited a player
• Fixed issue #1 View details of artefacts in the marketplace
• Fix: new marketplace items, tooltips and initial data loading
• Marketplace active for DEVELOPER and GAMEMASTER as default
• Marketplace must not be visible if the role/permission is not granted
• Fixed issue #127 (Usability Icons in Quest acceptance)
• Fixed issue #161 (thx @aabeling )
• Fixed issue #99 (password now editable by players)
• Issue #163 - button design and tooltips added

Happy new year and I hope you like the improved version! Please feel free to contribute if you like SonarQuest ;-)