Add connection testing endpoint

[petrdvorak]

Currently, the OAuth 2.0 flow does not provide any means of checking that the access token is still valid, and also there is no way to determine a connection name. This type of service is, however, required in couple more sophisticated frameworks, such as Spring Social, and for a good reason.

• I should be able to check if the connection is valid before displaying user information that the connection is valid (via for example bank logo in "Connected Banks" section).
• I should be able to assure that one user does not connect the same bank with the same account twice.
• I should be able to display a reasonable name for the connection in case there are multiple connections to the same bank (for example "Ceska sporitelna: Petr Dvorak").

Please provide an endpoint in a following format in the default auth realm:

GET /my/profile

WEB-API-key: 1234567891234567890
Authorization: Bearer 1234567891234567890

{
  "customerId": "ABC123",
  "firstname": "Jan",
  "middlenames": [
    "Baptista"
  ],
  "lastname": "Novak"
}