Merge pull request #11548 from RudyLu/keyboard/Bug902352-placeholder_as_word_separator

Bug 902352 - Make Gaia keyboard treats the placeholder
r=timdream(cherry picked from commit be95c3b6757290fff4fdde7a2b73c68f599131a1)
Bug 905950 - [Messages] Recipient assimilation should only occur when composing a new message r=gnarf

https://bugzilla.mozilla.org/show_bug.cgi?id=905950

- Restrict recipient assimilation:
    - Only when in #new view
    - Only when there is a placeholder to inspect

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>