Latte: implemented new macro {snippetRunner}

Adds ability to run some part of template without catching the output. Really useful with dynamic snippets. 

- adds ability to run dynamic snippets
- adds ability to run include with snippets

Discussion http://forum.nette.org/cs/5713-snippety-a-inkludovana-sablona#p73830 - see some requests for rebasing etc, it's really needed behaviour.

Also, see how it's possible to hack this without snipperRunner: https://github.com/nextras/datagrid/blob/master/Nextras/Datagrid/Datagrid.latte#L115-L117