Simplify session pool user id configurations

Here's a candidate solution (not yet decided though) from the mail thread.

The main point is the followings:

• The user id with '@...' looks hacky. The pool information should be separated.
• The delimiter, '@', doesn't look good.
• ...

So, a solution should cover the following usage scenarios. (By the way, (1) or (2) is preferable option. (2) should be in the default demo package.)

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1. A simple example with different credential infos.

binaries.repository.user.name = binary
default.repository.user.name = siteuser
writable.repository.user.name = admin

2. An example with extended pool information property (as Bart suggested)

binaries.repository.user.name = admin
binaries.repository.pool.name = binary # optional. this will be
concatenated with user id.
default.repository.user.name = admin
default.repository.pool.name = default
writable.repository.user.name = admin
writable.repository.pool.name = writable

3. An example with extended pool information

binaries.repository.user.name = admin@binary
binaries.repository.user.name.separator = @ # optional.
default.repository.user.name = admin@siteuser
default.repository.user.name.separator = @ # optional
writable.repository.user.name = admin::admin
writable.repository.user.name.separator = ::

I think the option (2) should be the default configuration in the demo
hst applications.
If so, it would satisfy everybody.

What do you think?