MNT: Make message consistent with emacs
ENH: Remove bog-citekey-action

`bog-citekey-action' generalizes the common setup (citekey selection
from notes or from user completion) of the citekey functions, but it
doesn't allow much flexibility for functions to handle citekey selection
differently. Replacing this with `bog-citekey-from-notes' shares the
citekey selection from notes but doesn't couple this to the user
selection.
ENH: Use stage for renaming BibTeX files

This avoids filtering all the names in the BibTeX directory to those
that match the citekey pattern, and it more consistent with how PDF are
renamed.
ENH: Remove path from choices when renaming PDF

Only files in `bog-stage-directory' are options, so the only relevant
information to present is the file name.