Started refactoring into templates. app_abstract + app_decore done.

Initial work on templating HTML output.

Provided ability to use placeholders with syntax [App:Name]
and also conditional output with <if placeholder="[App:Name]"></if>.

The app_decore function includes three inner templates for
antifeatures, categories, and permissions. The reason for these is that
my primitive templating engine does not support loops, nor do I think
it is worthwhile.
Templated main HTML (header, content, footer).

Still need to template the search/filter forms and the list of
latest apps.
Templated entire filter bar, including reset, keywords, license and categories.

Each of these is a different template, allowing them to be placed on
the page as separate blocks of content.
Almost finished templating all HTML.

Still have the error screen to template.

Also the XML of the atom feed could be templated, however I feel that
is less important because it isn't themeable and has to adhere to a strict
schema.
Merge branch 'master' into feature/templates

Conflicts:
	index.php
Minor fixes to default template after comparing to master branch.
Merge pull request #24 from pserwylo/feature/templates

Replace all HTML in index.php with templates