Simplify MainWindow UI

use QStackedWidget instead of multiple QSplitter childrens for the web and
HTML source views. This also makes the code for the splitter handling in
MainWindow simpler.
Improve perceived performance (#100)

Calculate the delay of the HTML processing based on the
number of characters in the markdown document instead of
a hardcode value of 100 ms.
Improve calculation of splitFactor

Take the handleWidth into account when calculating the split factor for
the QSplitter of the MainWindow. This prevents expansion of the right
view when the view is collapsed and the main window is resized.
Improve perceived performance (#100)

Do not update the web view when it is not visible.
Refactor MainWindow

* add syncWebViewToHtmlSource() method
* correct order in viewChangeSplit()
Add linux files to gitignore. Add qt generated files to gitignore
Ignore ui_ files and .moc files, too
Introduce tab width settings to options

Conflicts:
	app/optionsdialog.cpp
	app/optionsdialog.ui
Moving handler for tabWidthChanged to editor class. Fixed coding style error. Used QFontMetrics to determine tab width in pixels.
Merge pull request #108 from Slesa/gitignore-changes

Gitignore changes
Merge branch 'tabwidth-changes' of https://github.com/Slesa/CuteMarkEd into slesa-tabwidth-changes
Fix compile warnings
GroupBox for tab width option

Added groupbox for the new tab width option to the OptionsDialog.
Add "Word Wrap" action (#46)

add new entry "Word Wrap" to the "Extras" menu. With this entry the
use can change the line wrap mode of the markdown editor.
Word wrap in settings (#46)

Save and restore the en-/disabled status of the new word wrap
menu entry.
Merge branch 'feature/wordwrap-#46' into develop
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