[FEATURE] Custom ConfigurationManager with multiple PID resolves

Adds a new ConfigurationManager which loads a custom BackendConfigurationManager which contains multiple methods of resolving a page UID based on different URL arguments. Covers most cases in the TYPO3 backend where a PID does exist in some argument, but is not located in the `$_GET['id']` argument which is the only one the basic Extbase ConfigurationManager respects.

PID can be resolved from:

* GET.id
* POST.id
* GET.edit.$table.$pid (when *creating* records, $pid is expected PID)
* GET.edit.$table.$id (when *editing* records, $id is UID of record: load record from DB and read PID of record)
* GET.edit.$table.$id (when $table is `pages` then $id is PID, both when creating and editing pages)
* Currently active ContentObject record (very rarely filled in BE, included for completeness)
* TypoScript record's PID *if* there is only one active root TS record (which is how the current Extbase fallback works)

The result: failsafe PID resolving not just in Flux but every other extension, when Flux is installed.
[TASK] Raise minimum required TYPO3 version to 6.1
Merge pull request #445 from NamelessCoder/pageuidwoes

[FEATURE] Custom ConfigurationManager with multiple PID resolves
[TASK] Set version to 7.0-dev
[FEATURE] White/blacklisting allowed CTypes in Column and Area

Limits possible selections in the new content element wizard based on parameters defined in the Column or Area (or both) into which content is being inserted.

## Usage examples

In a content/plugin template:

```xml
<flux:grid.row>
	<flux:grid.column>
		<flux:form.content name="content">
			<flux:form.variable name="allowedContentTypes" value="text,textpic" />
		</flux:form.content>
	</flux:grid.column>
</flux:grid.row>
```

In a page template:

```xml
<flux:grid.row>
	<flux:grid.column colPos="1">
		<flux:form.variable name="allowedContentTypes" value="text,textpic" />
	</flux:grid.column>
</flux:grid.row>
```

Alternative syntax:

```xml
<flux:grid.row>
	<flux:grid.column colPos="1" variables="{allowedContentTypes: 'text,textpic'}" />
</flux:grid.row>
```

Using PHP (Flux Form Components):

```php
$grid = \FluidTYPO3\Flux\Grid::create();
$row = $grid->createContainer('Row');
$column = $row->createContainer('Column');
$column->setColumnPosition(1)
	->setVariable('allowedContentTypes', 'text,image');
```

To blacklist, use `deniedContentTypes` instead of `allowedContentTypes` as variable name. Both can be used together: first, the whitelist is applied if it has any types contained, and second, the blacklist is applied to remove elements from the list of allowed types (which is either the full list or the previously whitelist-filtered version, if a whitelist was specified).

Fixes: #197