Moved submodule discount to 3rdparty directory

Created a new directory '3rdparty' for modules from external sources.
Moved the git submodule discount to this new directory.
Update discount module to tag v2.1.7-cutemarked
Adapt qmake projects to moved discount module
Fix travis CI configuration after move of discount module
Move submodule hunspell to 3rdparty directory
Remove images and link to project website instead
Merge branch 'develop' into feature/autocompletion-#81

Conflicts:
	3rdparty/hunspell
	app/app.pro