Rewritten text selection (#3166)

* Improved text selection. Unhighlighting ctrl selects still broken.

* Removed the commented code.

* Removed the commented out code.

* Uploaded to wrong place.

* Uploaded to wrong place.

* Re-save with Unix line endings

* Same for the header

* Commented out more code to fix all known text selection and highlighting problems.

* This fixes #612 .

* Altered unhighlight() y1 declaration and assignment as requested. Also deleted 6 lines which were commented out.

* Removed all the scrollbar changes for issue #612. This now only handles text selection, and scroll bar changes are in a separate branch.

* Fixed drawing highlight box for double clicking a word.

* Altered ctrl click to select line on single ctrl click (Previously you needed to move the mouse to select the line(s).

* Unix line endings again

* Raise code to formatting standard

(use the clang-format tool with the .clang-format file at the root of the repository for this)

* Fixed ctrl-drag selection. Ensured ctrl-click selection worked too.

* Unix line endings