Merge pull request #142 from luhcas/master

Schaltflächen überarbeitet (fixes #131)
silently fail if an exercise type is not supported, fixes #141
don't iterate through null arrays, fixes #140
blocks can decide whether they are editable (blocks are editable by default), fixes #132
fix SQL query syntax, fixes #143
update LESS files, fixes #145
filter hash tags of newly created threads, fixes #146
add icon for blubber blocks, fixes #147
use ajax events to add filter hash tags instead of modifying any input elements
evaluate if a block is editable when it is displayed just after its creation, fixes #148
move postRendering of children to the #postRender method
htmlBlock tests and improved quick test
change video loading hint message, fixes #114
add cancel and save buttons where missing and use them to control the modification process of blocks, fixes #53
Farbanpassungen und Abstände angeglichen