Adds automatic functionality to the max-height for non-text items feature, and sets this as the default value.
Advanced tab spin box replaced with combo box.
Test coverage expanded on other functions in listpreviewwidget and pep8 errors fixed.
Fixed test naming.
Merged with trunk as of 2016-06-02_10:30.
lp:~knightrider0xd/openlp/non-text-item-height-default (revision 2674)
[SUCCESS] https://ci.openlp.io/job/Branch-01-Pull/1584/
[SUCCESS] https://ci.openlp.io/job/Branch-02-Functional-Tests/1...