Hide Activity option if Activity app disabled

[jotoeri]

Steps to reproduce

1. Disable Activity App
2. Create Announcement

Expected behaviour

The activities option should not be shown. The end-user won't know what it does.

Actual behaviour

One can choose to create activities or not.

Server configuration

Nextcloud version: 26.0.5
Announcementcenter version: 6.6.2

List of activated apps:

Activity DISABLED
Announcementcenter
[...]

[nickvergessen]

Same for notifications I guess

[mwinkens]

Same for Emails I guess, when no mailserver is configured