fix(translateService): fixes missingTranslationHandler-invokation bug

this fix makes sure that missingTranslationHandlerFactory only gets
called when there is no pending loader to laod translations asynchronously.

Closes #74
feat(translateService): removes empty options object requirement for loaders

currently, when using custom loaders for asynchronous loading,
you have to at least pass an empty options object to
useLoader(..).

now, when this comes in, you can leave it off when don't need
any optional options for you custom laoder
tests(midway): adds some midway testing
update version
Merge branch 'master' of github.com:PascalPrecht/ng-translate