Changed buttons in Heading Post Structure

Files for the structure, associated template, and webcontent using
this structure were changed. This changed adds an option to use
custom text inside of the button -- previously there was just a
default value of "view more". The three heading post webcontent
articles were also modified to show the three possiblilities of
displaying this button: custom text, default text, or no button.
Unique ids for Heading Post and Featurette

Templates for the two types of web content were changed. Previously
there was a div surrounding each type of article, and the variable
$content_class was part of the class attribute. However, this is
meant to be an ID attribute because it is unique for each article,
so this change was made.
Added Jumbotron site template

Includes two structures: jumbotron heading and heading post.
Jumbotron heading is the same as the structure from the jumbtron
(narrow) site template, just with fewer styling rules. Header post
is the same as the structure in the carousel site template, but
without the image option. Background color is specified in the
jumbotron heading template and may override theme settings. Text is
left unstyled for both structures -- can be specified in the theme.
Merge branch 'master' of github.com:noellekimiko/liferay-site-templates