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