Bug #727431 - Merge common factories' code into a superclass
[IMAPx] Enable concurrent connections

This returns back CamelIMAPXConnManager, and enables use of concurrent
connections with it, which helps with response time of user requests.
[IMAPx] Add "Number of concurrent connections to use" UI option
[IMAPx] Do not open each folder on LIST/LSUB responses

It has sever performance issues, especially with large folders,
which load (part of) the folder summary into memory too.
libebook: Don’t emit a warning on a dropped D-Bus connection in dispose

This occasionally and unavoidably happens in the libfolks unit tests,
where libfolks drops its final EBookClientView reference and proceeds to
kill the dbus-daemon. EBookClientView, however, keeps itself alive
internally in order to send a dispose() method call to the address book
server. This method call can return after the server has been killed,
and will return a G_IO_ERROR_CLOSED error in such cases. Ignore them.

https://bugzilla.gnome.org/show_bug.cgi?id=727784
libecal: Don’t emit a warning on a dropped D-Bus connection in dispose

See commit e31aae9c123da33a5613fa77cba55668e356f9ce.

https://bugzilla.gnome.org/show_bug.cgi?id=727784
Bug #722275 - IMAPX: Incorrectly reads astring values (mailbox names)
Always reject revoked certificates

If there is recognized a revoked certificate being used for a secure
connection, then reject the connection immediately, for security reasons.
This behaviour cannot be overwritten with a user's trust.
Bug #727237 - Correct LGPL license information in sources

I also added license information to source files where it was
missing and changed the way the license block is organized. All
the sources' license information comments follow the same pattern:

/* [ Optional short file description ]
 *
 * [ Optional copyright notices]
 *
 * License information block
 *
 * [ Optional 'Authors:' section ]
 */

The LGPL is references consistently now; source files with main()
function, like tests or D-Bus services, use 'program' in the license
information block, while the other sources use 'library' word.
[IMAPX] Do not expose user credentials in debug logs

And skip trailing \r\n in the io logs as well.
Bug #727598 - [IMAPX] Fails to list folders without NAMESPACE capability
Set properly children availability for newly created local folders

This is to help with a UI regression mentioned at
https://bugzilla.gnome.org/show_bug.cgi?id=722698#c13
with the local folders.
[IMAPx] Automatically limit maximum number of concurrent connections

In case a user has set more connections than the server has allowed,
the IMAPx may limit the connection count automatically, instead of
panic and close already established connections.