[Enhancement] Refactor of license django model (#187)

Fixes #119

Licenses are now created in the bootstrap management command. To only create the licenses use the command line argument `-ol` or `--only-licenses`.
These licenses are then fetched by there `cc_string` when adding a license to a package.

Co-authored-by: Liam Brydon <62733830+MyCreativityOutlet@users.noreply.github.com>
Co-authored-by: jebus <lorsbach@envipath.com>
Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#187
Co-authored-by: liambrydon <lbry121@aucklanduni.ac.nz>
Co-committed-by: liambrydon <lbry121@aucklanduni.ac.nz>

epdb/models.py

@@ -655,6 +655,7 @@ class ScenarioMixin(models.Model):
 
 
 class License(models.Model):
+    cc_string = models.TextField(blank=False, null=False, verbose_name="CC string")
     link = models.URLField(blank=False, null=False, verbose_name="link")
     image_link = models.URLField(blank=False, null=False, verbose_name="Image link")