Service and Storages not grouped by type anymore

Services and Storages were grouped by types in configuration file (and runtime variables). It was cumbersome (types set twice, more loops, etc.) and in the end useless.
`backupPath()` was also looping on all Services even though the Service to use is given as an argument.
I've removed type-grouping, making Service/Storage ID unique. Note that two Service/Storage cannot have the same ID (even if they are of different type), anyway it is enforced by YAML syntax.