Remove :tests from "use Dancer2"

This makes the tests work under Dancer2 0.141000
Replace deprecated Dancer2::Test with Plack::Test
Rewrite tests to use Plack::Test

This avoids using the deprecated Dancer2::Test
Test cache initialization done by check_page_cache

See https://github.com/yanick/Dancer2-Plugin-Cache-CHI/issues/5
Fix some uses of Dancer where it should be Dancer2

Also remove use of :syntax modifier that doesn't do anything.
move all tests to Plack::Test
plugin_setting() within a hook grabs the wrong dsl

Now I'm calling the $dsl object explicitly everywhere,
and get the config straight out of the app config.
grab the right DSL

fixes #5

a the commit.
release management
v1.6.0

 [BUG FIXES]
 - Have the plugin use the right DSL. (GH#5, reported by Kim Hansen)

 [ENHANCEMENTS]
 - Move tests away from Dancer2::Test and to Test::Plack. (Kim Hansen)

 [STATISTICS]
 - code churn: 10 files changed, 240 insertions(+), 195 deletions(-)