Support for custom Class ADMESerializers

teach ADME this new methods:
- ADME.registerADMESerializer(clazz, serializer)
- ADME.unregisterADMESerialier(clazz)

Now a custom data type can be stored in a column of the database by
defining its custom Serializer and registering it.

There's currently now way of associating a custom serializer to a
specific Field of an Entity: the configuration is global.
Make all sqlToJava methods return an Object (better for extendibility)

Reason I did this: suppose you want to define your own data type
ADMESerializer which convert the data into a String.
Would be good to extend the StringADMESerializer and just provide the
String/CustomDataType conversion. This is not possible if the
StringADMESerializer define "String" as return data type since you have
to return an object different from String.
Add Enum support: define the String and Int ADMESerializers

and rename unknownEnumName annotation parameter to fallbackEnumName.
Inprove javadoc for Serializers
Add ADMESerializers for BigDecimal and Currency classes

this are not defined as basic JavaType, they are more like examples on
how to define custom ADMESerializer.
Utility methods for defining a SQLiteContentProvider

a base SQLiteContentProvider, extracted from the source code of various
open source Android software and a class to more easily define your
ContentProvider Uris and construct your UriMatcher.