Don't link record in GridField form message

This is no longer allows through Form->sessionMessage() to avoid XSS.
3.0.7 changelog
Fix test relying on specific member title format.

If a custom member title format was used, the test would fail as it
only expected the default member title format.
API: Add attributes argument for CMSMenuItem.

Currently help menu item is the only external link in the CMS and the ability for it to work is hardcoded in the template. This request makes the target attribute definable by CMSMenu::add_link().

Adds documentation for how to add a basic external link to the CMS.
Merge pull request #2473 from ajshort/pull-1

Fix test relying on specific member title format.
Merge pull request #2474 from wilr/externalcmslink

API: Add attributes argument for CMSMenuItem for external links
BUGFIX: Without casting TreeTitle as HTMLText, unescape HTML appears in TreeDropdownField
Increased CacheTest time delay, avoid flickering tests

Setting a cache lifetime of half a second seems to be
unreliable on Travis when just waiting a second,
so let's wait a bit longer.
Merge remote-tracking branch 'origin/3.0' into 3.1
Merge remote-tracking branch 'origin/3.1.0' into 3.1
FEATURE: Disable specific tree nodes in TreeDropdownField

DO NOT MERGE: to be reviewed.

This feature request was born out of wanting the ability to disable (for example) a top level page from being selected, while still being able to select a child page. Using setFilterFunction() simply removes the node and its children.

Extra styling for disabled nodes

Disable ability to select a disabled node for TreeDropdownField

Disable hover CSS changes

Fixing merge conflict during rebase

Return a boolean for nodeIsDisabled()
Merge pull request #2037 from kinglozzer/feature-disable-treemultiselect-nodes

FEATURE: Disable specific tree nodes in TreeDropdownField