[FEATURE] Shortcut method to select top priority ConfigurationProvider

Before, there was only a method to select all ConfigurationProviders as an array. Now, there is a method to return only the topmost prioritised Provider. If multiple Providers have the same priority, the last one registered will be returned.
[TASK] Controller Base as API for Flux-enabled Controllers
[TASK] Move ContentService injection to AbstractFluxController

Also removes a few leftovers from migrating the AbstractFluxController from FluidPages
Merge pull request #55 from NamelessCoder/claus/abstractfluxcontroller

[FEATURE] AbstractFluxController to function as base API for Flux-enabled Controllers
[TASK] Add parameter containerExtensionScope to Configuration Service

Setting this parameter will override the plugin.tx_**extkey** part of the path when retrieving TypoScript configurations.
Merge pull request #56 from NamelessCoder/configurationservice

[TASK] Add parameter containerExtensionScope to Configuration Service
Merge pull request #54 from NamelessCoder/claus/getprimaryprovider

[FEATURE] Shortcut method to select top priority ConfigurationProvider
Merge pull request #53 from dreipunktnull/master

[BUGFIX] Fix translation of container elements