MBS-7771: Escape the content of textarea tags

Textarea fields that are prefilled with text containing HTML tags (or
otherwise using HTML reserved characters) hadn't this content escaped.
Most browsers accept this anyway and treat "<" as if it were "&lt;";
however, this means that it is treated the same as a literal "&lt;",
and both will be read as "<" when the form is submitted. This is a
problem in particular for link type documentation that may contain
HTML tags.

This is fixed by properly escaping all reserved characters, such that
"<" becomes "&lt;" and a literal "&lt;" becomes "&amp;lt;".
Escape the content of option tags
Fix double closing button tag
Add checks for valid HTML to link type edit tests

The controller tests for the link type and link attribute type edit
pages didn't check that the pages were valid HTML. These tests would
have caught the double closing tag fixed in the previous commit.
Remove spurious trailing slash from URL in test
MBS-6896: Stop requiring users to enter sortnames for non-artist entities
Use a linked_instruments in the WS2 controller

All the other entity types have a linked_... function in
MB::S::ControllerBase::WS::2 for loading additional entities related
to the main entity, so use the same model for instruments.
MBS-7744: Return alias type for all entities in WS2

Some entities (areas, instruments, labels, places, and series) had
specific code in their web service 2 controller for loading aliases,
instead of relying on the generic code automatically provided by
MB::S::ControllerBase::WS::2. This extra code did not provide any
additional features and, unlike the generic code, did not load alias
types, preventing them from appearing in the WS output. It is
therefore simply removed.
Add test for MBS-7744
Call collections collections instead of lists

Collections had a linked_lists function instead of linked_collections,
possibly for some historical reasons. Rename to avoid future
confusion.
Merge remote-tracking branch 'chirlu/mbs-7771' into beta

* chirlu/mbs-7771:
  Remove spurious trailing slash from URL in test
  Add checks for valid HTML to link type edit tests
  Fix double closing button tag
  Escape the content of option tags
  MBS-7771: Escape the content of textarea tags
Merge remote-tracking branch 'chirlu/mbs-7744' into beta

* chirlu/mbs-7744:
  Call collections collections instead of lists
  Add test for MBS-7744
  MBS-7744: Return alias type for all entities in WS2
  Use a linked_instruments in the WS2 controller
Merge remote-tracking branch 'bitmap/mbs-6896' into beta

* bitmap/mbs-6896:
  MBS-6896: Stop requiring users to enter sortnames for non-artist entities
Sidebar template: Set a default for a parameter

Make sure edit_links_add_entity is always defined in the
shared-entity-sidebar template, to avoid associated warnings.
Merge remote-tracking branch 'chirlu/fix_warning' into beta

* chirlu/fix_warning:
  Sidebar template: Set a default for a parameter
Uppercase locales as required by mmd-schema
Uppercase the locale in the test too.
Revert commits changing WS formatting, will instead change mmd-schema.
Fix up some label 'for' attributes in the link type form.
Change to table class wikitable, rather than border=1, to silence another html validator warning.