Merge PoExtractor & PoExtractor.OrchardCore into a single tool

[hishamco]

Now we have two tools which do the same things except PoExtractor.OrchardCore extend the first one by supporting liquid, while the intend of PoExtractor to extract translatable strings in Orchard Core, single tool is enough. We might extend this tool by having options to skip certain template

/cc @Skrypt

[lukaskabrt]

Just some notes from the history ...

• There used to be --liquid switch, but it was removed in #34
• Original idea behind two separate tools was not to force other consumers of the tool to take dependency on Orchard Core

[hishamco]

Thanks for your input @lukaskabrt

Original idea behind two separate tools was not to force other consumers of the tool to take dependency on Orchard Core

I expect that but while we are using the OC localization identifier conventions it doesn't make sense