Added search modes and extra functions

[wuniversales]

I have created a new search mode.
This could be considered part of a solution for the ticket #321

When activating the search, two search modes appear:

1- External mode.

This mode redirects and searches any external web page.

Features of this mode:

• Possibility of inserting the URL of a search engine.
• Configurable search parameter.
• Configurable form method.
• It is allowed to "Force" external search engines to only find results from the user's website.
• It is possible to open the results in a new tab.
• This is the mode activated by default since it does not require any api key.
• By default it is configured with duckduckgo, for obvious reasons of user privacy, but it can be configured with any search engine.

Screenshot:

2- Integrated mode.

This mode integrates searches on the user's websites.

Features of this mode:

• Use the previous internal search method.
• Configurable search parameter.
• It is possible to open the results in a new tab.

Screenshot:

[wuniversales]

It's ready

[candideu]

Thanks for this @wuniversales ! Works great!