Regexp tester app: Add link to help page

[ubacher]

RegExp Tester App:
It should be easy to add a link to a help page about regular expressions.

And maybe right in the window one could have a listing of all the special characters
which need to be escaped.

(Pressing F1 when in the app opens the help page for apps.)

[Mario]

There is already a link at the bottom. Probably you need to make the app window a bit larger: