OGM-348

Based on top of https://github.com/hibernate/hibernate-ogm/pull/235

This change offers a typed API to retrieve options from an `OptionContainer`:

    OptionsContainer options = ...;

    //retrieving unique option
    ForceExampleOption forceOption = options.getUnique( ForceExampleOption.class );

    //retrieving non-unique option
    Set<NamedQueryOption> queries = options.get( NamedQueryOption.class );

Internally, `OptionContainer` manages two maps (keyed by option type) for unique and non-unique options.

Note that the second commit (https://github.com/gunnarmorling/hibernate-ogm/commit/d6bf1429a530cee3d338c1c45a07c235869ba0dd) which removes `UniqueOption#getOptionIdentifier()` is not strictly required, I've created it as a base for discussion. Previously, the following would have hold true: 

    //identity solely based on the type
    ForceExampleOption.TRUE.equals( ForceExampleOption.FALSE )

This seemed quite irritating to me and also opens the door for subtle issues like this:

    //would be true also if actually FALSE was contained
    assertThat( optionsContainer ).containsOnly( ForceExampleOption.TRUE );