Mortgages section adding Help2Buy support

The new mortgages section where it helps work out your value % you own. Does not include option to add other mortgages into the total value calculation such as Help2Byy scheme rendering this section unusable. Needs option to add Help2Buy loan value into the mix.

I believe there has already been some discussion about this in recent posts here: Now in Labs: See your mortgage in Monzo 🏠 - #390 by RichardL