i18n: Rename all occurrences of "circles" to "teams"

[rakekniven]

On Transifex there are strings containing the word "circle".
These should be renamed to "teams"

[rakekniven]

There are references to "circles" in other apps as well e. g. polls and agora.

[sorbaugh]

Unsure if this fixes all occurrences, but see #2226