Merge pull request #357 from afuna/gmail-on-wrote-bug4196

(Bug 4196) Add more detection for the "On..." line
(Bug 5026) Add yyyy/mm/dd format
(Bug 5026) Limit how many lines back we look

To reduce the chance that we accidentally snip mid-message.
(Bug 5026) Another date format

On Apr xx, xxxx...
(Bug 5026) Recognize ---Original Message--- separator
(Bug 5024) Remove embedded HTML from the plaintext comment notif
Merge pull request #359 from afuna/plaintext-email-bug5024

(Bug 5024) Remove embedded HTML from the plaintext comment notif
Merge pull request #358 from afuna/general-on-wrote-bug5026

(Bug 5026) Recognize more formats of separators before the quoted message
Merge branch 'release-1.15' into develop

* release-1.15:
  (Bug 5024) Remove embedded HTML from the plaintext comment notif
  (Bug 5026) Recognize ---Original Message--- separator
  (Bug 5026) Another date format
  (Bug 5026) Limit how many lines back we look
  (Bug 5026) Add yyyy/mm/dd format