Hide page buttons when infinite scrolling is enabled

Switched currency converter to duckduckgo and added Bitcoin to currency list

- search.include_engines_path : add engines definition (doesn't replace the content of engines.yml)

doi.yml, engines.yml, locales.yml are loaded directly into doi, engines, locales (not more prefix)
some bug fixes on oa_doi_rewrite

- settings.yml has the same format as before
- doi.yml, locales.yml and engines.yml are loaded before (the disabled attributes are removed)
- if yaml search.engines path is defined, then all engines are disabled, and only engine specified in this list are enabled.
- settings.yml contans only general, search, server, ui sections. The search section contains the enabled engines.
- settings_robot.yml is unchanged

Fix findx engine

[fix] Force English results in Google when using en-US

Add pronunciaton of searx to README

[fix] Engine fixes

This solves a bug with Yahoo where some results don't specify
a protocol.

[mod] Refactor engine's search language handling

Add match_language function in utils to match any user given
language code with a list of engine's supported languages.

Also add language_aliases dict on each engine to translate
standard language codes into the custom codes used by the engine.

Add findx engine

Add languages supported by either all default general engines or 10 engines.

[fix] Change duckduckgo url to avoid error response

Fix Vim mode on Firefox

Change alpine version to permit ARM and amd64 deployment

[UI] fix custom-select in oscar

Firefox automatically opens a built-in quick search when user
starts typing without selected input and the Vim shortcuts
are not triggered

remove the option of sourcing manage.sh

Fix Microsoft Academic engine