Adds an archive command that moves the current message into the folder
specified in the account config entry.
Supports three layouts at this point:
- flat: puts all messages next to each other
- year: creates a folder per year
- month: same as above, plus folders per month
This also adds a "-p" argument to "cp" and "mv" that works like
"--parents" on mkdir(1). We use this to auto-create the directories
for the archive layout.
Consists of 3 functions
* Store: Access to MessageStore type
* SelectedAccount: Access to Account widget that the target widget
belongs to
* SelectedMessage: Current message (selected in msglist or the one we
are viewing)
Signed-off-by: Kevin Kuehler <keur@ocf.berkeley.edu>
