Fixed bug [ 1870906 ] There are few problems selection text by mouse in RichTextCt

Fixed bug [ 1870906 ] There are few problems selection text by mouse in RichTextCt
Fixed bug [ 1870265 ] window does not scroll after pasting text
Fixed bug [ 1870264 ] wxTextUrlEvent after click in empty space
Fixed bug [ 1806479 ] wxRichText URL issues (URL event triggered when clicking on blank space)
Fixed bug [ 1806953 ] wxRichTextControl::AddParagraph() is broken
Fixed a bug in SelectWord causing bad selections.
Added Ctrl+Backspace word deletion.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52110 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775