Prefetch request results #87

Song page beginning with 'A' : 96 -> 57 request
Prefetch request results #87

Song page beginning with 'A' : 57 -> 11 request
Section are not relevant in current_songbook context #87

Song page beginning with 'A' : 11 -> 8 request (actually related to my current_songbook...)
Cache artist songs #87

Artist page beginning with 'A' : 79 -> 55 requests
Use the cache of artist songs #87

Artist page beginning with 'A' : 55 -> 31 requests
Prefetch request results #87

Artist page beginning with 'A' : 31 -> 8 requests
Reuse artist slug #87

Cow-boy fringant page : 28 -> 10 requests
Reuse artist object #87

Cow-boy fringant page : 10 -> 9 requests
Merge pull request #89 from patacrep/reduce_request_2

Reduce number of SQL request (2)