[Mastodon] add a new search route

[SamR1]

In the current version, the search only retrieves toots with the keyword as hashtag (see Mastodon.timeline_hashtag).

=> add a new route to get toots from Mastodon.search, that retrieves keyword even it's not a hastag.
Note: the number of toots with the keyword as a hashtag seem to be much lower than those returned by Mastodon.timeline_hashtag.