support time range search

[fix] close #637 : the search box doesn't overlap the menu.

moving a comma

[fix] Close #640 : remove MapQuest maps.

[fix] deviantart engine xpaths

Fix anomalous backslash in string

These lines were added to fix a js image load issue (#535) what i cannot reproduce.
Hopefully we don't see it again

Add Google Scholar search engine

utils/fetch_currencies: fix comment

Add ScanR structures search engine

[fix] multilingual duckduckgo

only works if both country and language are set

In theory ScanR should also search for projects but the API is different,
so we'd need another engine.

Comparison to None should be 'if cond is not None:'

Fix whitespaces

Fix quantity of blank lines after code object.