Use a more recent and trustable network library

[davigonz]

After researching about the available Android network libraries out there and performing some tests by using our sample client app (more details in owncloud/android-library#51), we have finally made the decision to get rid of Jackrabbit WebDAV library and implement OkHttp 3.10.0

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TOPICS TO DISCUSS

1. Include tests by using OkHttp MockWebServer

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TASKS

1. Involving the app

• Adapt the new OwnCloudClient uses.
• Add dav4android link in Settings page.

2. Involving the library Replace Jackrabbit-webdav and deprecated/end-of-life HttpClient 3.1 libs with active and trustable WebDAV + HTTP client libraries android-library#51

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RELATED ISSUES

• Send a unique X-Request-ID header to allow tracing requests in apache and owncloud logs Send a unique X-Request-ID header to allow tracing requests in apache and owncloud logs #2055

• Multiaccount OAuth2 - basic Multiaccount OAuth2 - basic #2095

CC / @michaelstingl @jesmrec @theScrabi

[davigonz]

To be released in 2.9