OCR: Second Try based on user feedback

[seandenigris]

Use case:

• When OCRing a receipt, the amount, 12.43 is mistakenly read as 12-43.
• We know from the domain that there won't be a negative amount here, and certainly there wouldn't be a dash in the middle. The format must be something like: $?/d+(./d+)?
• The user indicates that this particular area on the receipt is an amount
• We want to retry to OCR just that area as an amount

How to do about this? Two ways that pop out are: 1) give a pattern to the engine?, or if we can't do that 2) restrict allowed characters to numbers and decimal (fairly straightforward with Tesseract - although there may have been a bug prior to 4.1)

Next question, who needs to do/know about this? In our OCR element, we currently have the capability for the user to say "this area should be an amount". Now we have the text and location. I guess for now we can put it in the the element. We want to:

1. See if the existing text is compatible
   2a. If it is, use it
   2b. If it isn't, re-OCR using some rules and try again (i.e. go to one, but don't get into an infinite loop)

CURRENT: Validation of number is embedded in visitor/reader - we should attempt to validate first?