match entry addons with mapping patterns

[importantchoice]

This pull request makes it possible to match mapping patterns against addons, defined by the user.

The description of my bank transactions often does not include enough information to uniquely identify the correct target account. E.g. my hosting provider requires only to include the invoice-number in the description.

So, it would be helpful for me to not only match the mapping patterns against the description, but also against arbitrary fields in the csv. As we can already parse those fields via addons, those addons can also be checked during the mapping process.