Improve Key Rollover management

[pitbulk]

• Be able to register future SP x509cert on the settings and publish it on SP metadata
• Be able to register more than 1 Identity Provider x509cert, linked with an specific use (signing or encryption
• Allow metadata to be retrieved from source containing data of multiple entities
• Adapt IdP XML metadata parser to take care of multiple IdP certtificates and be able to inject the data obtained on the settings.

[coveralls]

Coverage decreased (-0.07%) to 95.602% when pulling 728d51f on key_rollover_mngmt into f7a9652 on master.

[coveralls]

Coverage decreased (-0.9%) to 94.805% when pulling 701d65e on key_rollover_mngmt into f7a9652 on master.

[coveralls]

Coverage decreased (-0.9%) to 94.812% when pulling 701d65e on key_rollover_mngmt into f7a9652 on master.

[coveralls]

Coverage decreased (-0.9%) to 94.752% when pulling 650d2b9 on key_rollover_mngmt into f7a9652 on master.