submit button for arbitrary lines to prevent reactive cycle before input is complete

[denisovan31415]

couldn't get the boxplot SRC to work on BEE. error in the hline_arb_color argument value but this I think is likely due to not have the correct package versions on BEE. I don't want to install locally to test so I think this will best be done during next release UAT.

1: Propose update to the validate messages:
Arbitrary line input error: number of values, labels and colors must be equal.

2: Proposed update to validate logic:
noted that if there are 2 values then I don't need any labels but need at least one color. I think it would be much simpler if the logic was as reflected in the proposed new validate message. 1 value then 1 label and 1 color. 2 values then 2 labels and 2 colors. etc. wouldn't this be easier from a programming perspective too?

3: Propose reactivity flow:
Typing in the label looks like it's reactive with every key stroke. perhaps consider holding reactivity until user submits. I typed in "arb1 (25 U/L) and plot reacted to just about every key stroke so had to wait for 13 refreshes before it stopped. doing this could also benefit typing colors where plots throw a full on error when color is invalid value. would be good to trap invalid colors. maybe a vector of 20 valid colors to validate.

happy to get on hangout to discuss

Originally posted by @npaszty in #88 (comment)

[denisovan31415]

@npaszty

Issue is created from #88