Tidy up settings

[marcoambrosini]

Settings look a bit all over the place, I think we should left align everything and add clear descriptions of what these sections are about.

[juliusknorr]

Moving over to https://github.com/nextcloud/text_templates as this is not the text app settings but a separate one for snippets that can be used with the smart picker

[DaphneMuller]

@marcoambrosini please specify what text you would like where