Upgraded simpletest to v. 1.1.0

Commented out usages of $this->swallowErrors(); as it's not defined in simpletest anymore.
Fixed web_services test
Preserving now keys order in ElggData::$attributes
Ensured to store empty subtype as null instead of empty string.
Ensured that owner_guid, container_guid and access_id are kept as integer, not a string.
Ensured that access_id is kept as integer.
Adds ElggCoreUnitTest::assertIdenticalEntities() for entities comparison. Stores numeric entity attributes as integers.
Added simpletest for groups
Stores extended entity attributes as null when read empty from DB.
Removed simpletest swallowErrors() method calls as it's dropped in v. 1.1.0
Fix after rebasing branch.