Split search text by space, improve search

While doing the screenshots, I remembered that search for Félix d'Hérelle works with felix, herelle but not felix herelle. It is not a bug as the search module simply search for the whole string, and don't cut by space.

The idea is to return :

• Félix d'Hérelle collections when searching with felix herelle but also felix herelle, herelle felix
• λvir when searching with lambda λ, lambdavir but also lambda vir and vir lambda
• Félix d'Hérelle collections as first data source when searching felix collection
• prevent results pollution with d when searching for felix d herelle
• use tf-idf to sort results