Allow a theme to specify that it has *no* parent

[Aaron Wells]

Currently *all* themes (except the "raw" theme) either have another theme as their parent, or they default to having the "raw" theme as their parent. If a theme has no $theme->parent in its themeconfig.php file, then it gets assigned the "raw" theme as its parent.

The team that's working on switching our themes to the Bootstrap framework, say that it would be useful for their development work if they could make an "alternate raw" theme that does *not* inherit from the raw theme.

So I've implemented a patch that allows a theme to specify $theme->parent = FALSE in its themeconfig.php, to indicate that it has no parent theme.

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/4177

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/4177
Committed: http://gitorious.org/mahara/mahara/commit/b822b5673edb615c1fd34af3f131aaaa2d0b9331
Submitter: Aaron Wells (<email address hidden>)
Branch: master

commit b822b5673edb615c1fd34af3f131aaaa2d0b9331
Author: Aaron Wells <email address hidden>
Date: Wed Jan 14 17:29:38 2015 +1300

Let a theme specify that it has no parent

Bug 1410638. Currently, a theme that specifies no $theme->parent
in its themeconfig.php is forced to use "raw" as its parent.
With this patch, there are three options:

1. $theme->parent = false; : No parent theme.
2. $theme->parent = "sometheme"; : Sometheme is the parent
3. $theme->parent not defined at all: "raw" is the parent

Change-Id: Ibfeeae246b0f505b5759ee77eeed32467c464cab