chore(upgrade): enable site_notifications

when upgrading from elgg 1.8 to elgg 1.9 the site_notifications plugin
takes over the 'site' notification from the messages plugin. So enable
this new plugin if the messages plugin was enabled

Fixes #6468
chore(css): changed page menu item radius 

It is now in line with other rounded navigation elements
fix(css): selected page menu does not collapse sub menu
chore(travis): add 'deprecate' commit type

This type will allow us to easily call out deprecations in changelogs

Fixes #6785
Merge pull request #6794 from ewinslow/deprecate-b6785

chore(travis): add 'deprecate' commit type
Merge pull request #6790 from jdalsem/page-menu-collapse-css-fix

Page menu collapse css fixes
fix(core): no longer strip slashes on $_FILES and $_SERVER

When magic_quotes_gpc is enabled on your server file uploads would fail.

The Elgg_HTTP_Request class should only undo the magic quotes on the GPC
(GET, POST and COOKIES) super global not on other super globals (SERVER
and FILES)

Fixes #6777
feature(core): better registration of usersettings handlers

This will allow plugin developers to replace specific parts of the user
settings action without redoing part of the core actions.
fix(admin): show plugin settings menu on markdown page
Merge pull request #6788 from jdalsem/plugin-text-file-sidebar-menu

fix(admin): show plugin settings menu on markdown page
Merge pull request #6789 from jeabakker/enable-site-notifications

chore(upgrade): enable site_notifications
Merge pull request #6791 from jeabakker/elgg-http-request-magic-quotes-gpc

fix(core): no longer strip slashes on $_FILES and $_SERVER
docs(changelog): Move CHANGES.txt to CHANGELOG.md
docs(changelog): Better markdown formatting
Merge pull request #6804 from ewinslow/changes-b5798

chore(changelog): convert CHANGES.txt to CHANGELOG.md
docs(changelog): Fully updated CHANGELOG.md (to 1.9.0-dev)

Fixes #5798
Merge pull request #6805 from ewinslow/changes-b5798

docs(changelog): Fully updated CHANGELOG.md (to 1.9.0-dev)
chore(composer): pull version from composer.json

This would allow us to use grunt-bump to increase version numbers
programmatically to reduce release-process overhead.

Also opens to the door to install Elgg with composer:

```
composer create-project elgg/elgg ./path/to/elgg
```

Refs #6288
chore(release): conventional-changelog support

Refs #6783
Merge pull request #6807 from ewinslow/automate-b6783

conventional-changelog support