nmbug: move from contrib to devel

There seems to be consensus to use presence in contrib as
documentation of limited support by the notmuch developers; in fact
nmbug is pretty integrated into our current development process, so
devel seems more appropriate.

diff --git a/contrib/nmbug/nmbug b/devel/nmbug/nmbug
similarity index 100%
rename from contrib/nmbug/nmbug
rename to devel/nmbug/nmbug

diff --git a/contrib/nmbug/nmbug-status b/devel/nmbug/nmbug-status
similarity index 100%
rename from contrib/nmbug/nmbug-status
rename to devel/nmbug/nmbug-status

diff --git a/contrib/nmbug/status-config.json b/devel/nmbug/status-config.json
similarity index 100%
rename from contrib/nmbug/status-config.json
rename to devel/nmbug/status-config.json