Mission Planner silently accepts nonsensical numbers based on locale

I have the latest version of MP and was trying to add a parameter as "12.34". Since I am in a locale where commas denote decimals, MP decided to silently parse that number as "1234", which is very much the wrong thing to do.

As people don't generally enter thousands separators in parameters, MP should parse both a comma and a period as a decimal separator, to reduce the possibility of such errors.

Related: #128

Start by reproducing parameter entry with "12.34" in a comma-decimal locale, then trace the Mission Planner code that parses entered parameter values. The issue is done when comma and period decimal separators are handled without silently turning the value into 1234, with behavior covered by an appropriate regression test if the project has one.

Written by the indexing model from the issue text.