Make ServiceConfiguration constructor to be private

Also move ServiceConfiguration header to src/oauth2 folder
Remove exception throwing in ServiceConfiguration methods
Merge pull request #35 from Melzas/add-oauth2-configuration

Add OAuth 2.0 Configuration class
Add and partially implement OAuth 2.0 Service

add Service class
implement Service constructors and getAuthorizeUrl method
move ServiceConfiguration header to include
Add tests for getAuthorizeUrl method of OAuth 2.0 Service class
Add OAuth 2.0 Token class
Implement getAccessToken method, create stubs for getAccessToken* methods

implement getAccessToken method
create stubs for getAccessTokenAuthCodeGrant, getAccessTokenImplicitGrant, getAccessTokenOwnerCredentialsGrant, getAccessTokenClientCredentialsGrant
Implement OAuth 2.0 Service signRequest method
Add test for OAuth 2.0 Service signRequest method
Make buldable under gcc 4.8.1

exceptions after asserts added, otherwise complier was complaining about "control reaches end of non-void function"