prepare menu items and code for navigation history
add simple navigation view history browsing, ref #135
#135 implemented view history class and moved to AbstractNavigation
ref #135 add history saving for trackball manipulator
merge new master into navigation history branch, ref #137
resolve merge conflicts, ref #137
limit navigation history to 128 items, ref #135
clean up navigation history code, ref #135
change to 4 spaces standard
change previous/next to current object if last/first, ref #135
fix segfault on history browsing, ref #135
compare to viewhistory object, not only viewmatrix, ref #135
change member variable id to timestamp, ref #135
fix comparison of viewmatrix, ref #135
fix segfault on undo, ref #135
add qtcreator project files to gitignore
Revert "add qtcreator project files to gitignore"

This reverts commit d277cb6e5ee54062b481b466f36a9e46451786a0.
add qtcreator project files to gitignore
add ALL qtcreator project files to gitignore
fix multiple issues in viewhistory logic, ref #135