#70 Check that user submitted values are sane

[Drew]

Some values should be checked for sanity. EG: you can
enter 36 instead of 1.036 for a fermentable ppppg. In
this case, the UI should convert 36 to 1.036 before
setting the ppppg, or report an error. Acceptable
range should be 1.000 to 1.050.