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

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 bff41987a49af9ae53ff9fc3494fa7973ac03500, reversing
changes made to d08108be6293c8764f0d1d950a7aab283cddffed.

This reverts commit 79ceb13577fcc83eabe642a4ed6dd793b7bf0d4b, reversing
changes made to eaa0fb8102825fa4ccdb348429fdbf39837921be.

[mod] upgrade versions in requirements.txt

[fix] extract_text: use html.tostring instead html_to_text.

search.py : Fix and some minor modifications

If no language is specified, bing returns results with multiple languages
for one query which isn't really useful. Setting english as default
insted if nothing.

[fix] change modal glyphicon arrows to image icons

[mod] add a search_one_request_safe function wrapper

CSS modal window for image results

Changes in search language list (continuation of #748)

that support them.
users can still query lesser supported through the :lang_code bang.

[mod] Allow users to search in most engine supported languages