Add message indicator applet support

So first, could you explain to me what features evolution shps in the message indicator?

e.g. what entries does evolution show in the message indicator? things like setup mail and just having a button there that opens the mailapp would be relatively easy. Having the live unread messages in there, probably requires more work for each of the providers and wouldnt work without having codable plugins shipped with each mailer.

However, I am not sure all webmailers even provide an rpc api or something to query for unread mails. So we might end up with a fragmented featureset, with some webmail providers only having basic support while others have message preview, and unread message count info etc.

if you want drop reference/api manual URLs here for webmail provider that have that ;) ... might come handy if someone (or me) wants to pick up this bug at some point.

I would prefer if desktop-webmail avoids needing users to enter their passwords. I don't store my mail credentials anywhere.

I doubt you can show unread message counts and new mail notifications without having the user's credentials. Besides, there's lp:gm-notify for gmail. Wouldn't it be better to extend that project to support different email providers?

However, it could be useful for desktop-webmail to put _something_ in that mail spot.

This page shows the Evolution indicator:
http://frugalware.org/~devil505/blog/?p=1632&lang=en

So there are several items:
- Mail
- Compose New Message
- Contacts
- email accounts

Seems like it would be nice to have Mail open your account and compose open a new message. Contacts could open your contacts page ( http://www.google.com/contacts ), but I don't know if that's a simple link for all of the supported webmail providers.