Application review overview and invites

[seanjparker]

Following from issue #7 we need to be able to rank the applications by the highest rated to the lowest and have the information displayed in a table on the Rating | Overview page.
On this page we need the following features:

• List of all the applications, the name of applicant and the total average score (mean average of all the reviews for an applicant)
• "Batch invite" button which will load a model
• Model will have an input for how many people we want to invite to the hackathon alongside some options (maybe tick boxes?) that allow us to choose keeping whole teams together (if > 1 person in team has made the invite cutoff, then invite the whole team)
• The model also allows to get a count of how many people will be invited using the currently selected options