Sync: Part 9 sync to upstream

[rnr]

This sync PR contains next:

• Added alpha for color to the whitelabel script to expand configuration options
  chore: added alpha for color to whitelabel edx/edx-mobile-marketplace-ios#87

• Configurable colors on Learn Tab (doesn’t change colors for upstream)
  chore: Elm theme improvement on course home edx/edx-mobile-marketplace-ios#86
  chore: Elm theme improvements on Learn Tab edx/edx-mobile-marketplace-ios#88

• UI improvement on Course Discussions
  chore: Elm theme improvement on Course Discussions edx/edx-mobile-marketplace-ios#90

• UI improvements for modals and alerts (below is only one UI change)
  chore: Elm theme improvements for modals and alerts edx/edx-mobile-marketplace-ios#91

• Сonfigurable resume button. Also fixes missed arrow on Resume button
  chore: configureable resume button edx/edx-mobile-marketplace-ios#92

[codecov]

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