#4 POFileSpell: Only check against installed dictionaries

[Bewied]

Currently, there is no sanity check against the list of available dictionaries,
and apparently no limit in the amount of errors produced.

This has the undesired effect that every word for every language (for which I
don't have an appropriate dict installed) is reported as misspelled.

I'd like to suggest a new feature --no-missing. When this flag is set and POFileSpell detects that a dictionary seems to be missing, only output a single warning for that language, probably along the lines of "No dictionary found for language es_AR. You can specify additional dicts with the --dict=path/to/dict option."

With this flag, the output can be kept more concise and meaningful. To reinforce the point: 1 warning among 100 false-positive warnings is useless.