Add Quota to Connectivity View (#2612)

* add imap::get_quota_roots()

* schedule quote-checking job on getting connectivity-html

* get quota and debug print it

* basic quota output

* update quota at most once per minute, emit event on changes

* use more meaningful names

* add some comments, move update_recent_quota() to quota.rs

* show root name only if there are several roots

* make clippy happy, some refactorings

* allow only one update-quota job per time

* add now supported QUOTA to standards.md

src/lib.rs

@@ -75,6 +75,7 @@ pub mod peerstate;
 pub mod pgp;
 pub mod provider;
 pub mod qr;
+pub mod quota;
 pub mod securejoin;
 mod simplify;
 mod smtp;