Add syntax highlighting for fish shell

Summary:
FEATURE: 381396

For fish shell version 2.7.1

References
http://fishshell.com/

Reviewers: Framework: Syntax Highlighting, dhaumann, cullmann

Reviewed By: Framework: Syntax Highlighting, cullmann

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: Framework: Syntax Highlighting, Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D20233