clang-format git hook and formatting

I really like this project and plasma mobile, and I would like to contribute.

• A git hook has been added to check formatting upon committing, as advised here https://api.kde.org/ecm/kde-module/KDEClangFormat.html (the hook is created during cmake configure time)
• clang-format has been run and minor formatting issues fixed.
• headers have been reordered consistently, following recommendations from: https://techbase.kde.org/Policies/Frameworks_Coding_Style#Includes
• Also member initialization has been ordered like their declaration order (-Wreorder)

Hope this will be helpful.