Make no. of communities per pagination / expansion configurable

[mark-cooper]

References

• Resolves #1749
• Resolves #1750

Description

Adds new config settings for no. of communities to display on the home page & community-list page.

Instructions for Reviewers

Compare result of updating the config, for example:

browseCommunities:
  communityListPageSize: 25
  topLevelPageSize: 10

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
• [ ] My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• [ ] My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• [ ] 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.