bug#21857: package install should give better feedback

[David Reitter]

When installing a package, give an acceptable “XXX successfully installed” 
message in the echo area as the last message.
As it is, it seems to just show a “done” for the last dependency, which is 
confusing or uninformative.

Also, if the *Packages* buffer is present--which it will be because the user 
may have picked the package to install after doing M-x list-packages—this 
buffer should be updated to show that the package was installed.

(Observed in master branch, installing JDEE from MELPA.)