HTMLPurifier filtering

- Replaced == with === to avoid type juggling
- Removed unneeded TODO
- Added HTMLPurifier to composer.json
- Added Service to allow singleton instance of purifier.
- Implemented use in Customer Controller Search function.

Signed-off-by: objecttothis <objecttothis@gmail.com>
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f