[MainUI] fix type "number" for list separator in Designer

[DarkC35]

Fixes #949

After changing the separator type to text it works as intended but there was one problem in following use case: when you need a space ' ' as separator character/string, the updateParameter method interprets it as a non-NaN value (since isNaN(' ') is false) and resultet in a NaN as input string. (This also occurs on other text inputs when you type a space, like url, refresh, frequency, ...)

I tought about two ways to solve this:

1. Only check for isNaN when type="number" (like in the second commit)
2. use isNaN(parseFloat(value)) instead of isNaN(value), since parseFloat(' ') === NaN so the check would work. This way had one problem when the number of space characters is important because parseFloat(' 1') === 1 and this will trim leading whitespaces of the input.

[relativeci]

Job #18: Bundle Size — 10.88MB (~+0.01%).

ac6636d vs f4fc2a8

Changed metrics (1/8)

Metric	Current	Baseline
Cache Invalidation	0.84%	85.77%

Changed assets by type (1/7)

	Current	Baseline
JS	8.55MB (~+0.01%)	8.55MB

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View Job #18 report on app.relative-ci.com

[ghys]

LGTM, thanks