Fetch/save/load account name and avatar URL

[chanseokoh]

Fixes #24.

Account name and avatar URL are queried through Google OAuth2 API. Basically, you do

Oauth2 oAuth2 = Oauth2.Builder(...).build();
Userinfoplus userInfo = oAuth2.userinfo().get().execute();

and the result userInfo contains an email, an account name, and an avatar URL. Very convenient.

(userInfo already contains an email, so the previous low-level logic to directly accessing https://www.googleapis.com/userinfo/email and manually parsing the response is no longer necessary.)

Notes:

• Email cannot be null, as before. Name and avatar URL may. If an email cannot be retrieved for any reason, login is considered failed.
• UserInfoService is a wrapper around Oauth2.Builder and Userinfoplus. The new class is to enable unit testing, since Mockito cannot mock some of the OAuth2 API classes. (They are final.)
• URL --> String for avatarUrl: after some tinkering, it looks like String is better suited.
• Query timeout is now set through HttpRequestInitializer.

[chanseokoh]

Also, account name and avatar URL are persisted.

[elharo]

Is this still active? If so, please merge with master and ping me to review. Otherwise, close. Thanks.

[chanseokoh]

This is active but has never been a priority. Hope I'll get back to this sooner or later.

[codecov-io]

Codecov Report

Merging #32 into master will increase coverage by -3.21%.

@@            Coverage Diff             @@
##           master      #32      +/-   ##
==========================================
- Coverage   78.09%   74.88%   -3.21%     
==========================================
  Files           8       10       +2     
  Lines         210      223      +13     
  Branches       24       20       -4     
==========================================
+ Hits          164      167       +3     
- Misses         38       50      +12     
+ Partials        8        6       -2

Impacted Files	Coverage Δ
...in/GoogleAuthorizationCodeTokenRequestCreator.java	0% <ø> (ø)	:white_check_mark:
.../google/cloud/tools/ide/login/UserInfoService.java	0% <ø> (ø)
...ava/com/google/cloud/tools/ide/login/UserInfo.java	0% <ø> (ø)
...va/com/google/cloud/tools/ide/login/OAuthData.java	100% <100%> (ø)	:white_check_mark:
...om/google/cloud/tools/ide/login/AccountRoster.java	100% <100%> (ø)	:white_check_mark:
.../tools/ide/login/JavaPreferenceOAuthDataStore.java	85.41% <100%> (+1.32%)	:white_check_mark:
...java/com/google/cloud/tools/ide/login/Account.java	94.73% <100%> (+12.38%)	:white_check_mark:
...google/cloud/tools/ide/login/GoogleLoginState.java	70.87% <88.23%> (+0.18%)	:white_check_mark:
... and 2 more

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[chanseokoh]

Ready for review, @elharo.