Input check

[enh] validate input and raise an exception inside search.py. The exception message is output in json and rss format.

[mod] add a __common__ template that can't be selected but that provides a common place for shared templates.

What has been moved into this template :
* opensearch*.xml is always the same whatever the themes.
* the text inside */about.html

Semantic Scholar

[enh] show spelling corrections

[WIP] Add 1337x.to engine

[fix] searching for "!google_images text" doesn't work

[mod] /config API : add more fields for each engine

[mod] /config API : add language_support, paging, safesearch, supported_languages, time_range_support, timeout fields.

Remove pyasn1-modules from dependencies

According to https://github.com/kennethreitz/requests/issues/749#issuecomment-19187417 there is no need to install pyasn1-modules.

[enh] standalone_seax.py is a command line interface to searx

Revert CSS image modal

[fix] fix standalone_search.py

[mod] ./manage.sh can download geckodriver

This reverts commit bff41987, reversing
changes made to d08108be.