add chart-testing default config and updated apt packages

[hajowieland]

Fixes #16

• Added the chart-testing default configs (chart_schema.yaml, lintconf.yaml) so no configs need to be provided
• Updated apt packages to latest available versions

# ls -lah /etc/ct
total 16K
drwxr-xr-x 2 root root 4.0K Jan 29 10:22 .
drwxr-xr-x 1 root root 4.0K Jan 29 10:23 ..
-rw-r--r-- 1 root root 1017 Jan 29 10:22 chart_schema.yaml
-rw-r--r-- 1 root root 1.1K Jan 29 10:22 lintconf.yaml