[doc][client] Add a link to a setup instruction page as reference.
[UserConfigView] Change the URI specification.

The previous URI form is '/userconfig/itemName'.
This way needs to request multiple times when the multiple items
are gotten. This is not-so-happy story.

The new way can get multiple items at once and reduces the number of
communications.
[UserConfigView] Can accept a POST request to store configuration items.
[UserConfigView] Clean up.
[UserConfig][view][test] Add a new test: test_store_and_get().
[UserConfig][view] Remove a debug print line.
[UserConfig][view][test] Add an assertion to check the returned content.
[UserConfig][view][test] Delete all data in the database to make a condition be the same always.
[HatoholUserConfig] Add a method: get().
[HatoholConnector] Send a CSRF token automatically when it is needed in this layer.
[client][test] Fix the wrong usage.
[HaotholConnector] Enable to specify dataType and contentType.
[UserConfigView] Send items to be saved in a JSON format.

UserConfig provides a feature that accepts any type of data
as a value.  Naturally, JS code that is the client wants to
store/get without the conversion to/from a string to make it simple.
[client][test] Remove a debug print line.
[UserConfig][View][test] Add a new test: test_store_multiple_items_and_get().
[UserConfig][View][test] Clean up.
[UserConfig][View][test] Clean up.
[UserConfig][View][test] Clean up.
[UserConfig][View][test] Clean up.
[UserConfig][View][test] Add a new test: test_store_multiple_items_and_get_with_non_existing_item().