Remove food routes

[fosterfarrell9]

Note: This PR should be merged after #749.

Important

After you have performed the migrations included in this PR, run rails solr:reindex, so that solr obtains the new values for the media sorts (in particular, this needs to be done in production).

This PR removes the food routes (that seemed funny when the project was still a little toy project) by serious-looking routes and resolves #456.

"Kaviar" => "LessonMaterial",
"Erdbeere" => "Erdbeere",  # stays the same
"Sesam" => "WorkedExample",
"Kiwi" => "Repetition",
"Nuesse" => "Exercise",
"Script" => "Manuscript",
"Reste" => "Miscellaneous"

Notes

• I stayed with the name erdbeere since this exists as a project of its own.
• In order to let this (already big in terms of files changed) PR not to get too big, I did not remove the references to the THymE player. This is supposed to be done in a later PR. Also, we would need a new name that replaces THymE.
• There should now be some refactoring possible, in particular related to the methods media_types, media_sorts, media_names in application_helper.rb (they are used only in a small number of files) and also medium_sort in lecture.rb. For PR size reasons and better refereeing experience I decided not to do these refactorizations in this PR; instead they should be part of a later PR.

Todo

• Update migration timestamps to more recent date.

[codecov]

Codecov Report

Attention: Patch coverage is 47.05882% with 27 lines in your changes missing coverage. Please review.

Please upload report for BASE (dev@e6e9a7b). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
app/models/lecture.rb	37.50%	10 Missing ⚠️
app/models/medium.rb	52.94%	8 Missing ⚠️
app/controllers/media_controller.rb	0.00%	4 Missing ⚠️
app/helpers/application_helper.rb	0.00%	4 Missing ⚠️
app/models/tag.rb	0.00%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             dev     #754   +/-   ##
======================================
  Coverage       ?   54.28%           
======================================
  Files          ?      178           
  Lines          ?     7498           
  Branches       ?        0           
======================================
  Hits           ?     4070           
  Misses         ?     3428           
  Partials       ?        0           

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