renamed PHPCRBlockLoader to PhpcrBlockLoader

| Q             | A
| ------------- | ---
| Bug fix?      | no (cs bug)
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | - (doc does not mention this class)

simply adjusting to code standards.