Batch of fixes and new features:

    - Implemented dialog icons using font awewsome (#758)
    - Implement drop down toggle in WMenu (#1756)
    - WMessageBox and WDialog: properly document and implement escape and default buttons (#1822)
    - Improvements to WDateEdit (#2075)
    - Various fixes and improvements to avoid build warnings with pedantic compiler settings
Merge commit 'github/master'