pushkey: introduce an ``decodekeys`` function This function provides a standardized way to exchange pushkey content over the wire.

wireproto: use pushkey.encodekey

pushkey: introduce an ``encodekeys`` function This function provides a standardized way to exchange pushkey content over the wire.

bundle2: add more phase movement in the test To test phase exchange with bundle2 we need some phase movement to happen. Appropriate logging is added to track those changes.

bundle2: use non-publishing repo in test If we are going to test usage of bundle for phases exchange, we need some phase movements to be exchanged.

bundle2: use a smarter template for test We use a more compact template that includes phase information.

getbundle: declare type of parameters In addition to listing the expected options for ``getbundle``, we also list their types and handle the encoding/decoding automatically. This should make it easier for extensions to transmit additional information to getbundle.

bundle2: introduce a ``caps20to10`` function This function factors the creation of appropriate entries to use in ``bundlecaps`` argument of ``getbundle``. This cleans up code calling ``getbundle`` and helps its usage in more part of the code.