using our own 500px key and using okhttpclient.
fix oauth page cannot register issue...

it seems no need registeration, but, fix it...
refactors for timeline adapter' s thubm option.

1. use enum, no string equals, it could be more effient.

2. add two annotaion, @NotNull and @Nullable, makes a helper facility.
small refactors for tweet adapter.

add another constructor for more explicit.
refactors for the tweet timeline' s prefs.

so far, so good, just register the pref change in adapter, much better than before.
refactors for the timeline prefs.

1. fix last commit bug, small/medium pref changes bug.
2. add tweet detail image pref, offline no pic downloaded.
refactors for the comments timeline.

add line on the bottom.
refactors for tweet timeline.

1. fix emotion icon awful display on different screen size device.
2. some small improvements.
add a back to top func in timeline.
add no history to the welcome activity, for smooth

also, put the auth in a new no-history activity.
adjust thumbs width on large width.

max width -> 480px
finish v0.8.1, merge to master branch.