Add max sentences to Test by Generation

[rosypen]

Add the ability to specify the maximum number of sentences to generate on the Test by Generation Options page.

This should probably be a list of preset options (eg. 25, 50, 100).

Then this value can be passed to the ACE command using the [-n count] option (https://github.com/delph-in/docs/wiki/AceOptions)

The idea here is to control the potential explosion of generated sentences.

[goodmami]

The -n option is how many outputs per input, not how many outputs total. But limiting the number of outputs with -n AND controlling how many inputs you send to ACE seems like an effective method of limiting the results.