Submit button added to POST form

Added Submit button to generated POST form to allow manual submit
in case user has JS disabled
Merge pull request #120 from tpazderka/submit_button

Submit button added to POST form
Allow urls instead of file paths for cert_file, ca_certs and key_file configuration parameters.
Removed unused import
cert_file, key_file and ca_certs should point to a file with the certificate not the certificate itself.
Fixed attribute filtering logic, take 2.
Fixed decryption/verification of signed and encrypted assertions.
Made a special idp version compatible with uwsgi/gunicorn usage.
Sha2 changes and some spring cleaning.
Script that merges several metadata streams into one.
If statement already is a string do mess with it.
Updated some documentation
Added merge_metadata.py to scripts to be installed.
Added dumps method to MetadataStore, changed merge_metadata.py to take advantage of this.
Fixed some remaining issues
Allow choice of output type.
Don't mind empty lines.
Fixed problem with signing metadata.
Switched back to what it should be.
Upped the time slack, should I rather have a 'don't care about the time validity' ?
When not a SAML class instance adding an element is slightly more complex.