Email: Remove the "Message text size" setting item from general settings.

GeneralPreferences should not call PreferenceScreen.removePreference()
to disable text_zoom preference which is not its direct child.
The Email text size will be matched the System settings. So there needn't
show the setting item.

Now text_zoom preference is an unnecessary item, we will remove the
reference code and xml content for it.

CRs-Fixed: 620377

Change-Id: Idfb49f2c929a5a86458060f149eee7f2b971d158
Email: Do not delete the message from server if the user set it as "Never"

Checking the pop3 account's delete policy when delete the mail.
If the user set the delete policy as "never", then we needn't to
delete the mail from server, but only delete the mail from local.

CRs-Fixed: 625820

Change-Id: I77abd62e079e46f0a77961e7c9eab6ca94a59ec2
Email: Cache the attachment during downloading

When download an attachment, cache it into the content resolver.
So that the cached data could be reused instead of downloading
it again for everytime.

CRs-Fixed: 601682

Change-Id: Ia34bc4e69967ec78916535d270de36fe2a71f932
Email: Notify UI data changed of the unread mailbox.

Notify UI the data has been changed of the unread mailbox and UI will
update the content according to the new data.

CRs-fixed: 630974

Change-Id: I041d2638c8c4c892e6207cdac7dd89edf34d511f
Email: New a receiver to handle the checking mail action.

As the recevier need protect the checking mail action by a permission,
but the receiver also handle the secret code action which couldn't
protected by the permission. So we need move the checking mail action
to a new receiver and handle it.

Change-Id: I5e3a5f36ba2512ac8970d3f7650cee16d58d768f
Email: Display the load more view at the bottom of the mail.

 - Display the load more view at the bottom of the uncompleted mail.
 - Save the viewable parts/attachments to Attachment table. And according
   to the viewable attachments' contentId to update the message's body.
 - Notify the mail list to update if the mail's attachment flag changed.
 - Do not show the viewable attachments in the preview interface.
 - Update the sync size configuration item's layout.

CRs-fixed: 642921

Change-Id: I7d349daaf562fe65dfde9baedf69845722a24feb
Email: Do not show "Sending feedback" item if the uri is null in general settings

Caused by not set "Send feedback" invisible when feedback uri is null
in general settings.

Add the judgement to set "Send feedback" invisible when feedback uri is null.

CRs-Fixed: 620380

Change-Id: I062487bd2eb9c64d497bda42a2eaef78bb775db7
Email: Encoded the name of the attachment files.

Caused by the file maybe not named by the English alphabet.
So accroding to RFC822, need encoded it.

CRs-fixed: 648698

Change-Id: I5c0d337323b6db28bfa51abfb732e2f8bc25735f
Email: Update sync status for mailboxs which not load from server.

For IMAP and POP3 account, there are some mailbox do not load the data
from the server. If the user try to sync them, it also need update the
sync status for these mailboxs to refresh the UI.

CRs-fixed: 652818

Change-Id: Ibcc0b4c29832120d3d9285e93adc143cfb7b1e56
Email: Add a summary for "Confirm before forwarding"

Since there is no summary for the setting "Confirm before forwarding",
it might be difficult for the user to find out how it works.

Add a summary for "Confirm before forwarding" to explain more details
about this setting preference.

CRs-fixed: 652151

Change-Id: I29f6a303c1b65a53682ffb8dcd1576d513ac1ff0
Email: Hide the feedback button if nowhere to feedback

The string value of email_feedback_uri in strings.xml presents where
to submit the feedback. If it is empty or invalid, shall hide the
feed back button.

Add the switch to check email_feedback_uri to show feedback button for
the Email module. Add the switch to set the capability for UnifiedEmail
to use.

CR-fixes: 667335

Change-Id: Ia01350417b0b020b03093212ea7ef0ff2d655fe9