Make text fields in table cells

[BryceStevenWilley]

Splitting the part of #31 that isn't fixed off.

We don't make things that look like table cells into text fields, and we should. We already have the boxes as a part of the connected components, we just need to filter them. The best approach would be a combination of:

• what boxdetect does: see if X% of the pixels inside of the box are 1, if so it's likely not a text field
• see if there are pixels that are 1 in the middle of the box, i.e. not in the top (right, left, or center).

[nonprofittechy]

Let's sync up with the thoughts here: SuffolkLITLab/docassemble-ALWeaver#96

An idea that I had for the Weaver is using the + symbol to indicate linked fields. I can't find the issue where I suggested it though.