Take minimum_makers config var value into account on Send page

[theborakompanioni]

Closes #101

This PR fetches the minimum_makers config variable and uses it as minimum amount of collaborators on the Send page.
This means a taker operation cannot be started with a lower value than what is specified in the config file.

One little caveat is that the initial value for the amount collaborators is randomized between [5, 7] (min +1, min +3), which can lead to the initial value not being shown as active button in the CollaboratorsSelector component.

Is this acceptable for now? What do you think?

Screenshot for minimum_makers := 2:

Also, the approach of parsing an error message from text/html is removed as this has been fixed in joinmarket-clientserver#1170

Edit: this also does not take into account if the value is greater than 99 - which is the default maximum amount. Guess that is an unreasonable value and can therefore be ignored.

[theborakompanioni]

This is what the CollaboratorsSelector component looks like with the default value 4 for minimum_makers:

[ghost]

Nice change! Yeah I'd say we can live with the 99 being hardcoded for now. 👍

[ghost]

Cool! ✅