add checksum verification for web file attachment (rebase)

To test this,
1. choose a file
2. find out its SHA1 hash (e.g., use shasum on it)
3. attach it to an image using the web client
4. download it
5. check that the file locally still has the same hash as before
6. in the originalfile table in the database find the file (e.g., by name) and check that
  - the hasher is correct (should be SHA1-160)
  - the hash is correct
  - the size is correct.

For instance, select of.size, ca.value, of.hash from originalfile of, checksumalgorithm ca where of.hasher = ca.id and of.name = 'myfile';

rebases #1077