BLOCKER: Allow multiple templates per raw data

Multiple fixes in the PR:
- Allows multiple prep templates per raw data
- Preprocessed data is now linked with prep template rather than raw data
- Fixes #326 
- Changes on initialize.sql:
  - SPECTRA removed
  - SFF added
  - FASTA -> FASTA-Sanger

This PR allows @antgonza to continue with his PR.
I think what @wasade meant is to use the SQL idiom `IF EXISTS` see this [link](http://stackoverflow.com/a/7887033/379593).

```sql
IF EXISTS (....)
  DROP TABLE ...;
```