Merge pull request #178 from bajasoft/master

Hide quick search with Esc key, fixes #129
Use custom MDI widget for now, fixes #170
Try harder to not let ReloadOrStopAction action to be disabled, hopefully fixes #149
Allow to open downloaded file by pressing enter
Use load() instead of setUrl(), somehow fixes #87
Minor consistency fixes
Raise error when trying to use Qt older than 5.2
Move handling of quick search to WebWidget so it could be shared by multiple modules
Initial draft of Importer API
Add FilePathWidget class
Use FilePathWidget in preferences dialog
Merge remote-tracking branch 'upstream/master'