Join with commas rather than spaces

Previously, the collection of context initializers was joined with a
space.  This should have worked, but the error seen when using this
configuration implies that comma-delimiting class names is the only
supported way.  This change joins the collection with commas instead
of spaces.

[#49695345]
Merge 49695345-fix-failure to master

[Completes #49695345]
Add auto reconfiguration to Play applications

Previously, auto reconfiguration was limited to web applications only.
This was not by design, but was the case in practice.  In the auto
reconfiguration support, Play applications can be reconfigured
(although in a more limited way) and this support was not used
properly.  This change splits the auto-reconfiguration support into a
'Spring' side and a 'Play' side.  The supported JAR is the same
regardless of which kind of reconfiguration you are getting, but the
detection and modification behaviors are quite different.
Merge 49696097-play-auto-reconfiguration to master

[Completes #49696097]
Auto reconfiguration framework documentation

Previously, the two auto reconfiguration frameworks were not
documented separately.  This change updates to documentation to
reflect the new dual implementations.

[#49696097]
Merge 49696097-play-auto-reconfig-docs to master

[Completes #49696097]
Merge commit '69476007414fb831b4e8fc5cda08c4190606c48c'