Email: Use */* mime/type on add_attachment

This change replace the current intent type passed to ACTION_GET_CONTENT (image/*) for a more
properly */* intent type. This allow add/request to pick any kind of files (not only images).

Change-Id: Iaf596590cbbe42d6f088db61222afa495ea7d9fc
Email: Display a more proper message when attachment has no size

This change proposes to distinguish between when the attachment has more than the max size and
when attachment has no size. Actually, one common message is display for both checks.

Patchset 2: Added DvTonder suggest

Change-Id: Iaba70d61a8f7242feb7e9ef1d2d3625aa85a071d
Issue 6748: Unable to download ZIP (and many other filetypes) files attached to emails

Issue: http://code.google.com/p/cyanogenmod/issues/detail?id=6748

This change allow the user to select which extensions of the UNACCEPTABLE_ATTACHMENT_EXTENSIONS
defined by AOSP should allow/disallow from attachment download.
A new General->Security setting was added with a multi select list preference with
all the extensions. By default all the extensions will be marked as blocked.

Patchset 3: Rename disallowed to blocked. Cleanup.

Change-Id: I19e6ff96d6251c5edc77b89dd8c44db1342677fa