[keycloak-dev] Use default methods in Provider and ProviderFactory

[Stian Thorgersen]

The life-cycle methods on providers and provider factories (init, postInit,
close) are frequently not used, but providers have to add empty methods. To
reduce the amount of boilerplate in a provider I propose changing the
following to have empty default methods:

ProviderFactory:
* init
* postInit
* close

Provider:
* close