Add new pages

[Redande]

• Move old teachers-page to teacher-guide
• Add new teachers-page
• Add learning environment-page
• Add research-page
• Add about us-page

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 66.43%. Comparing base (da04de4) to head (3c6c2c9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1258 +/- ## ======================================= Coverage 66.43% 66.43% ======================================= Files 144 144 Lines 6042 6042 Branches 1434 1434 ======================================= Hits 4014 4014 Misses 1889 1889 Partials 139 139 ``` | [Flag](https://app.codecov.io/gh/rage/mooc.fi/pull/1258/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rage) | Coverage Δ | | |---|---|---| | [backend](https://app.codecov.io/gh/rage/mooc.fi/pull/1258/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rage) | `66.43% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rage#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.