Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

 templates/oscar#	gelöscht:       searx/static/themes/oscar/fonts/glyphicons-halflings-regular.ttf

* drop image_layout.js from simple theme
* move image_layout.js to oscar theme and delete common js dir (since its empty now)
* align top position of image detail modal with bottom position of search header
* use flexbox to display images; row height can be set via @results-image-row-height in defenitions.less
* display span title underneath each image with a max width of 12rem
* increase margin and padding around image article on desktop and tablet
* make article height smaller on phone layout (height of 6rem) to display more content on current view
* remove content from result, if the title and content matches
* use a group that cotains the flex image article, if images are mixed with other categories
* fix pylint issues in webapp.py
* use the default.html result template in unit tests (thanks @return42)

* oscar theme: code from searx/plugins/infinite_scroll.py
* simple theme: new implementation

Co-authored-by: Markus Heiser <markus.heiser@darmarIT.de>

When an image is selected, the detail with the full size image is displayed
on the right side of the screen (or full screen on tablet and phone).

When Javascript is disabled, the thumbnail is a linked to the full size image,
as it was before.

When the image proxy is enabled, the full size image is also proxied,
in consequence this commit increases the bandwidth usage of instances.

The detail can be closed by the close button or the Esc key.
It is possible to go to the next and previous images using the j and k keys
or the button on the top right of the screen.

prepare the code the PR #90

Adjust thumbnail sizes to fill the container width

In webapp.py, there is a new function "get_translations" lists available translations

Close #2064