chore(apps): move icons into the apps folder (#3139)

* chore(apps): move icons into the apps folder

* rename to `icon.png`

* replace solr image

* remove `docs/` from gitignore

* move app specific docs into app folder [skip ci]

* fix some links

* chore(apps): update image links temporary

charts/stable/calibre-web/Chart.yaml

@@ -8,7 +8,7 @@ deprecated: false
 description: Calibre-Web is a web app providing a clean interface for browsing, reading
   and downloading eBooks using an existing Calibre database.
 home: https://github.com/truecharts/apps/tree/master/charts/stable/calibre-web
-icon: https://truecharts.org/_static/img/appicons/calibre-web.png
+icon: https://truecharts.org/img/appicons/calibre-web.png
 keywords:
 - calibre-web
 - calibre