MULE-7050: MuleApplicationClassLoader loadClass() method not synchronized

_Adding synchronizing FineGrainedControlClassLoader#loadClass(String,boolean)
_Removing  MuleApplicationClassLoader#loadClass(String, boolean) override
_Adding test to verify the fix
_Renaming FineGrainedControlClassLoaderTest to FineGrainedControlClassLoaderTestCase
Merge pull request #143 from mulesoft/MULE-7050

MULE-7050: MuleApplicationClassLoader loadClass() method not synchronize...