Replaced a few calls to stringr with stringi (which has to stay for unicode encoding function). Not likely that people won't have stringr, but makes the dependencies a little better.

Also adds regexplain_web()

- Removed knitr parameter
- Add result_only (not in knitr)
- Soft deprecate kntir parameter
- Separate group.css from other css styles

and restore when input$pattern is empty

- Use global option regexplain.addin.max_lines (default 100)
- Give hint on warning about option
- Always use unique lines in selection

regexplain.debug.gadget.(text|pattern|replacement)

and allow overriding default help text when loading server side help section

and move octals to hex group (yeah, I know)

Can't interact with global app elements from within a module

Goal: gadget input and output text boxes show actual tokens in string (one backslash == one backslash). Input box takes regular regex.

for consistency with base and stringr argument names. Left "Send regex to console" button text same for consistency with tabs in gadget.