Sugar functions for objects

[sebffischer]

As the current consensus is to provide sugar functions for the classes, I suggest the following:

• oml_data(...) --> OMLData$new(...)
• oml_task(...) --> OMLTask$new(...)
• oml_flow(...) --> OMLFlow$new(...)
• oml_run(...) --> OMLRun$new(...)
• oml_collection(...) --> OMLCollection$new(...)

I prefer these names over the shorthand forms that we usually use, or at least I could not quickly come up with names that don't sound stupid.