project owners aren't aware there are proposals they should review

[Martin Pool]

raof reported that some projects (that do actively use launchpad) end up with multiple merge proposals filed, but not noticed by the project maintainer, therefore inadvertently neglected.

<RAOF> Oh! He also raised a point that I hadn't run across - apparently merge requests are, by default, not very visible to maintainers.
<RAOF> He'd interacted with an upstream maintainer who went "Oh, my! There are all these merges people have asked me for?!"

Possibly approaches to address this (more study needed):
 * making sure that project owners are notified of new proposals if (or "even if") nobody is subscribed to the branches
 * highlighting pending proposals on the project home page
 * a 'work you need to do' concept in the ui
 * sending reminder mails about outstanding work (would need to be done very carefully)