This introduces notmuch-jump, which is like a user-friendly,
user-configurable global prefix map for saved searches. This provides
a non-modal and much faster way to access saved searches than
notmuch-hello.
A user configures shortcut keys in notmuch-saved-searches, which are
immediately accessible from anywhere in Notmuch under the "j" key (for
"jump"). When the user hits "j", the minibuffer immediately shows a
helpful table of bindings reminiscent of a completions buffer.
This code is a combination of work from myself (originally,
"notmuch-go"), David Edmondson, and modifications from Mark Walters.
