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/imap/scan_folders.rs

@@ -102,7 +102,7 @@ impl Imap {
     }
 }
 
-async fn get_watched_folders(context: &Context) -> Vec<String> {
+pub(crate) async fn get_watched_folders(context: &Context) -> Vec<String> {
     let mut res = Vec::new();
     let folder_watched_configured = &[
         (Config::SentboxWatch, Config::ConfiguredSentboxFolder),