csv import: strip commas from number fields on importing

**Is your feature request related to a problem? Please describe.**
When importing a formatted number such as 1,200 into a number field, an error is thrown

**Describe the solution you'd like**
If the commas were stripped before the import this could alleviate this issue occurring.

**Alternative solution**
Is to strip the commas manually before upload, but this can be tricky, as google sheets displays commas when they don't exist, and libreoffice doesn't display commas in numbers when they do exist (by default)