Reduce concurrent server calls.

Add error logging to server

- Attachments bug should be mostly fixed now
- You first see a preliminary version (shows "Downloading: <filename>"), while we're downloading the attachments.

In addition to the extensive changes in 0.6:
* French translation
* Dutch translation
* Fix bug where copying several messages to Local Folders would lose exactly 1 message. Does not happen when copying between Exchange folders, only when copying to Local Folders or POP3 accounts.
* Report server errors that happen during sending mail

Major bug fixes and speed improvements.

Features:
* Attachments: Show when the Exchange server deliberately blocks an attachment due to its file type, per administrator policy setting
* Show folders that are not children of the inbox

Performance:
* When opening a folder for the first time, now show the headers roughly 100 times faster
* When downloading message data, adapt number of parallel calls to server limits
* Improve performance of contact resync

Big fixes:
* Detect logout situation better
* Better error logging on Error Console (Ctrl-Shift-J)
* Refactor license logic code
* Detect when creating 2 OWA accounts at the same server and prevent it

* Fixes critical security issue. Exposure is very limited, because JavaScript is disabled, so there is no known way to cause actual harm with this bug, but just in case there's a way to exploit this, we ship this fix.
* Now blocks remote images as expected