Customizability of theme colours

[davide-negretti]

References

• Fixes #1914

Description

This PR fixes some issues related to the base and dspace theme colours.

Instructions for Reviewers

• Bootstrap uses a semantic colour scheme, that associates each colour to a meaning (primary and secondary colour, warning, info...).
  • The badges in the MyDSpace used Bootstrap classes badge-MEANING classes to change these colours.
  • I created new classes that allow to decouple the colour of the badges from the semantic colours.
  • Previous badge-MEANING classes are still available and their colour is still the one defined in $theme-colors
• The colour variables for the navbar bottom margin were not correctly used.
  • Before:
    • --ds-header-navbar-border-bottom-color was defined as green for the base theme
    • the base theme ignored this value and used grey instead
  • Now:
    • --ds-header-navbar-border-bottom-color is defined as grey and it is used by the base theme
    • --ds-header-navbar-border-bottom-color is overwritten with green for the dspace theme
• Primary color was changed from blue to dark by redefining the value of blue. The blue colour has now been restored, and primary colour is now defined from a different variable.

Checklist

• [x] My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• [x] My PR passes TSLint validation using yarn run lint
• [x] My PR doesn't introduce circular dependencies
• [x] My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• [x] My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• [x] If my PR includes new, third-party dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.