Support twitter bootstrap by setup script

solve #25

Changes
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Major changed files are following;

- https://github.com/tokuhirom/avans/pull/26/files#diff-0
- https://github.com/tokuhirom/avans/pull/26/files#diff-1
- https://github.com/tokuhirom/avans/pull/26/files#diff-2
- https://github.com/tokuhirom/avans/pull/26/files#diff-3

Other changes are adding bootstrap and jQuery.

Why do I change archetype descriptor from `archetype.xml` to `archetype-metadata.xml`?
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`archetype.xml` cannot specify directory means we must enumerate the all of files. It makes tend to be redundant, so switch to `archetype-metadata.xml`.