fixes #1033 

Namely:
- Only match messages which start with exactly "/me ".
- Simplify the match, checking a string instead of a complex regex.
- Always remove the first four characters in the case of a match, to not
leave an extra leading space.

Fixes #1188.

This will eventually allow client-side theming support.

This helps languages which use a different typography for the colon,
such as French which has a narrow non-breakable space before it, or
Japanese which uses a full-width colon character.

Otherwise we get `TypeError: Cannot read property 'extend' of undefined`
when attempting to extend `BootstrapModal`.

This is both lighter, looks better when rendered at arbitrary
resolutions (as there is no scaling being done), and actually editable
for different deployments.

This image has been hand-drawn using the PNG as a background.

fixes #1264

Also...

- hide the badges in overlayed view mode
- hide the features list in overlayed view mode

Currently translated at 73.7% (261 of 354 strings)

Translation: Converse.js/Translations
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/nb/

Currently translated at 99.4% (352 of 354 strings)

Translation: Converse.js/Translations
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/fr/

Currently translated at 99.4% (352 of 354 strings)

Translation: Converse.js/Translations
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/fr/