Improve the Fortran fixed format syntax highlighting

Summary:
3 improvements:

• Restore the comment highlighting when using the "!" character (comment all the line after the !, works whatever the position of the !)
• The characters after the 72th column are highlighted as comments (they are ignored by the compiler)
• The continuation character is highlighted (5 firsts characters are blank and the 6th is not blank and not a number, usually "&" or "*")

Test Plan: Check the updated autotests/input/highlight.f

Reviewers: nibags

Reviewed By: nibags

Subscribers: nibags, kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D22253