Remove the following alternate forms of commands:
* aliasing A -> B
* unaliasing A -> B
* implicating A -> B
* implicate A -> B
* unimplicating A -> B
* unimplicate A -> B
* updating A -> B
* change A -> B
The following forms are accepted:
* create alias A -> B
* alias A -> B
* create implication A -> B
* imply A -> B
* remove alias A -> B
* unalias A -> B
* remove implication A -> B
* unimply A -> B
* update A -> B
Only downcase tags in aliases, implications, and category change
commands. Don't downcase mass update commands. Mass updates are
potentially case sensitive (for example: `mass update source:imageboard -> source:Imageboard`).
* Don't raise exceptions when a BUR is invalid. Instead, use Rails
validations to return errors. Fixes invalid BURs potentially raising
exceptions in views. Also makes it so that each error in a BUR is
reported, not just the first one.
* Revalidate the BUR whenever the script is edited, not just when the
BUR is created. Ensures the BUR can't be broken by editing. Fixes a bug
where forum threads could be broken by someone editing a BUR and
breaking the syntax, thereby causing the BUR to raise an unparseable
script error when the forum thread was viewed.
* Validate that removed aliases and implication actually exist.
* Validate that the tag actually exists when changing a tag's category.
* Combine bulk update request processor unit tests with main bulk update
request unit tests.
The name AliasAndImplicationImporter is a holdover from the time before
bulk update requests existed. This was a bad name because it doesn't do
any actual importing, instead it's used for parsing and executing bulk
update requests.
