Allow export as PDF for single plan session

[Teo230]

What problem does this solve?

There is already a dedicated feature present in the latest release about export as PDF but only for the weekly plan (#149)
Here I want to ask to add the same functionality for the single plan session

Proposed approach

Add an export button as PDF for single plan session

Dependencies

• This doesn't require adding a new dependency

[DuarteSantos8]

Thanks @Teo230, done in v1.3.9: in the routine editor you can print a single routine or save it as a PDF, on the web and in the app.

Released in v1.3.9: https://github.com/DuarteSantos8/openGym/releases/tag/v1.3.9