added message upload support.
added advanced option to create local-only folder.
disabled sync & push for local-only folders.
hid expunge, check_mail, and "Load up to x more" for local-only folders.
hid create/rename/delete folder options for webdav (someone give me a webdav account).
added advanced option to change if a folder is local-only or syncable.
add dialog to confirm clearing local messages, and if it should include local-only messages or just synced messages.
added advanced option to automatically upload on move from local-only to syncable.
changed background color in message list and subject color in message view of local-only messages.
changed: keep local-only messages in folders no longer on server instead of deleting folder, and mark folder as local-only.
added automatically fully downloading messages moved/copied to local-only folder.
added advanced options option (if not enabled, those settings will be hidden).
reworked onCreateFolder(), onRenameFolder(), onDeleteFolder().
added Store.isAppendCapable().
added LocalFolder.expunge() [unused].
