💄 [#1529] Improve contact-form styles

[jiromaykin]

Contact form needs icon in select + different placeholder text, and styles for textarea.
https://projects.invisionapp.com/share/UF134RWMWCK8#/screens/471596624
In order to just change the Select styles, I needed to break open the form and turn it into a render_form.

Side Note: all Selects in the entire projects should 'actually' have a muted style, but it is impossible to do this with CSS if all fields have a value AND are not 'required' (or else all of the Options inside the Select will look muted) - only required and invalid values can be targeted with CSS across most common browsers.
"...The problem is that these elements have very different default looks across browsers, and while you can style them in some ways, some parts of their internals are literally impossible to style..." (new issue nr.#1556)

[codecov-commenter]

Codecov Report

Merging #667 (24c8b86) into develop (47aeb4f) will increase coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 24c8b86 differs from pull request most recent head 77cb4ae. Consider uploading reports for the commit 77cb4ae to get more accurate results

@@             Coverage Diff             @@
##           develop     #667      +/-   ##
===========================================
+ Coverage    96.24%   96.26%   +0.01%     
===========================================
  Files          631      631              
  Lines        22474    22466       -8     
===========================================
- Hits         21631    21627       -4     
+ Misses         843      839       -4     

Impacted Files	Coverage Δ
...en_inwoner/components/templatetags/contact_tags.py	100.00% <ø> (ø)
src/open_inwoner/openklant/forms.py	100.00% <ø> (ø)

... and 2 files with indirect coverage changes

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[jiromaykin]

@Bartvaderkin it seems the "ContactFormTestCase" test is faling - wondering which field causes this problem?