C++ API: remember last selected figure with figure("name") when calling
commands.
VIBes viewer: added the "view" action, which sets the current view box.
It also supports automatic zoom.
VIBes-viewer: added the --show-open-dlg command line option that shows
an "open file" dialog to select the file to read at startup.
VIBes communication now uses ".vibes.json" file in the user profile
directory (updated server and C++ API to use HOME or USERPROFILE
environment variable). Solves #24.