Add init command handling

What this PR does:
+ adds catchall task (had trouble trying to run `cleaver init` with previous version of code)
+ adds cleaver init functionality:
User is prompted for presentation's title, his name, twitter handler, output file.
`cleaver init lolz` will be assuming title of Lolz, lolz.md as input file and lolz.html as output file.
Username is either git username or last part of ~ directory name
Twitter handler default is username
Output files default is downcased title + '.html'

Needs: 
+ proper testing on another environment,
+ omission (maybe?) for empty properties (so, if I make something empty, it doesn't appear in output file)