fix(members): prevent members search with empty query
fix(rss): River entries include their full correct summaries again

This causes the rss viewtype's river/item view to fall back to the
item's default viewtype in order to capture custom logic that
determines what the summaries should be, since the river's summary
view (`river/elements/summary`) doesn't know how to handle all
possible river items, especially now that we have a `target` field
in the river.

Fixes #6901
chore(notifications): remove docs referring to annotation/relationship support

Closes #6837
fix(deprecation): the deprecation wrapper correctly handles array access

When array access is used on the wrapper, the wrapper now checks the wrapped
object for ArrayAccess. If found, it uses that instead of property access.
This also emits deprecation warnings on array access, which were left out
accidentally.

Fixes #7017, #6917
chore(twitter): cleans up Twitter API to work with 1.9 session

This updates the session handling to use the new elgg_get_session and set/get/remove
rather than the deprecated array access. Also cleans up ElggSession a bit.
fix(thewire): More effective textarea change detection
Merge pull request #7021 from Srokap/pr/7020

fix(thewire): More effective textarea change detection
Merge pull request #7018 from mrclay/7017

fix(deprecation): the deprecation wrapper correctly handles array access
Merge pull request #7015 from ewinslow/river-rss-b6901

fix(rss): River entries include their full correct summaries again
Merge pull request #6970 from ewinslow/notifications-docs-b6837

chore(notifications): remove docs referring to annotation/relationship support
fix(notifications): Corrected html entities handling for email subject and body

Fixes #6905
Merge pull request #6978 from jdalsem/members-search-blank

fix(members): prevent members search with empty query
Merge pull request #7016 from mrclay/6917

chore(twitter): cleans up Twitter API to work with 1.9 session
fix(groups): give feedback if a user cannot be added to a group

Fixes #6081
Merge pull request #7022 from beck24/6089-group-join-action-message

fix(groups): give feedback if a user cannot be added to a group
feature(discussions): Added email SMTP headers for better thread grouping.

Additionally changed message subjects for group discussions to make Gmail happy.

Fixes #6894
fix(release): Corrected release script Windows system compatibility
Merge pull request #6965 from Srokap/ticket_6909

fix(notifications): Better threading + resolve html entities decoding issue
chore(i18n): update translations
chore(release): v1.9.0-rc.4