[js] update jquery.corner.js to the latest version (uses native css support for browser that provide it); closes #1625065

[js/css] remove old versions of ui.tabs/slider etc.; closes #1625085

[devtools] make return value of get_response_header(raw=True) consistent wrt get_header(raw=True) i.e. get_response_header(raw=True) now returns the first element of the list rather than the list itself.

[widgets] handle no value label for tristate radios, put default separator on class for easier redefinition - closes #1624839

[doc] update of the update

[tz postgres support] we've to commit the connection once time-zone is set, else we may loose the setting

[tz support] more tests

[dataimport] actually commit every desired number...

[doc] major update of the install documentation

[facets] make rangefacet comply with start_unfolded (closes #1615869)

[testlib] make a clear distinction between input / output HTTP headers The get_header() / set_header() API is the same as for CubicWebRequestBase : - get_header() returns the **request** header - set_header() / add_header() works on the **response** header FakeRequest adds two additional methods : - get_response_header() returns the **reponse** header - set_request_header() adds a **request** header FakeRequest now uses the `headers_out` ineherited from CubicWebRequestBase. It also uses a `_headers_in` attribute

[entity] create_entity/cw_instantiate should initialize entity's cache to avoid later queries