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