Do not overwrite OAuth session if already present.

`Session` and `SymfonySession` should not set `lusitanian_oauth_token`
on instantiation if it already exists.
Add tests for session storage constructors
Merge pull request #81 from popthestack/master

Do not overwrite OAuth session if already present.
Merge pull request #82 from gigablah/session-test

Add tests for session storage constructors
improve readme with packagist badges and composer info
Merge pull request #84 from toin0u/improve-readme

improve readme with packagist badges and composer info
Bug fix - First argument should be service name

As defined in the TokenStorageInterface src/OAuth/Common/Storage
Readme update - Tumblr is OAuth 1.0

Tumblr is OAuth 1.0 https://github.com/Lusitanian/PHPoAuthLib/tree/master/src/OAuth/OAuth1/Service

Not found on the OAuth2 dir https://github.com/Lusitanian/PHPoAuthLib/tree/master/src/OAuth/OAuth2/Service
Removed deprecation warnings from foursquare

Foursquare requires you to pass a query variable `v=YYYYMMDD` that specifies the last date that your api implementation was checked against.
Add `Common\Http\Client\AbstractClient`.

`Common\Http\Client\StreamClient` should extend the new `AbstractClient`.
Remove `maxRedirects` and `timeout` from constructor and set default directly on class.
Add setters for `maxRedirects` and `timeout`.
Move `normalizeHeaders` to `AbstractClient`.
Add `Common\Http\Client\CurlClient`.
Add `ServiceFactory::setHttpClient()` class method.

 * Remove `ServiceFactory::__construct`. HTTP client should be set via
`setHttpClient`.
 * Remove `$httpClientMap` as it's not longer necessary. `setHttpClient` enforces
that the client implements ClientInterface via type hinting.
 * To maintain backwards compatibility, `ServiceFactory::createService` creates a
`Common\Http\Client\StreamClient` instance if no HTTP client has been set.

I'm not crazy about the backwards compatibility hack, but it keeps the library
functioning the way it did before while at the same time adding flexibility.
Add `CurlClient` to `HttpClientsTest`.
Add PUT request support to `Common\Http\Client\CurlClient`.
Add support for other HTTP methods in `CurlClient`.
Added Amazon and PayPal examples
Added Dropbox example and fixed Base API URL error for Dropbox service.
Changing the service() visibility on AbstractService, added Google Login scope
Merge pull request #87 from thomaswelton/patch-1

Readme update - Tumblr is OAuth 1.0
Merge pull request #91 from flavioheleno/master

Dropbox service fix and Amazon/Dropbox/PayPal examples