Feature/jump to screen

[Tazovsky]

PR introduces:

• jump to screen buttons (named jumpBtn):
  
• buttons prevBtn, nextBtn, firstBtn, lastBtn which are wrappers around shiny::actionButton - thanks to that click actions can be easily observed in server
• run example app from inst/examples/06_jump_controls to see introduced changes
• when reviewing diffs please turn on following, because something went wrong with line ending conversion in RStudio:
  

[juba]

Hi, thanks for your PR and sorry for not answering it sooner.

Unfortunately I have some work to do on shinyglide, in relation with #8, and I think this may interfere with your PR, so I prefer not to merge it for now. But I'll take a look at it as soon as I find time to work on the package.

Thanks again.