fix github callback url

my bad, <your-site> wasn't displayed, looks confusing with it
string ending fixed
handle cURL errors
fix translation
fix button trans
typo
typo
missing string added
Merge pull request #58 from Remo/patch-4

fix translation
Make access_token_secret nullable

For now this column is not being used. 

It is mainly for other social providers that might be added in the future so it could be erased all together or made NULL by default.
Merge pull request #56 from Remo/curl-exception-handling

handle cURL errors
Merge pull request #55 from Remo/patch-3

string ending fixed
Merge pull request #54 from Remo/patch-2

fix github callback url