Move session init functionality into init.php

Issue #98.
Move login init functionality into init.php

Issue #98.
htaccess: Export a HTML_ROOT variable

Issue #98.
template.php: Remove $template_dir constant

Issue #98.
template.php: Remove $template_ext constant

Issue #98.
template.php: Remove $twig_autoloader constant

Issue #98.
template.php: Remove double newline

Issue #98.
template.php: Add pip_template_get_default_engine()

Issue #98.
template.php: Add pip_template_get_template()

Issue #98.
template.php: Remove globals

Issue #98.