documentation: Created new "Getting Started" manual.

Creation involved removing the overview-manual and replacing it
with the getting-started manual.  All links to the string
"&YOCTO_DOCS_OVERVIEW_URL" had to be replaced with
"&YOCTO_DOCS_GS_URL" across the entire YP manual set.  I renamed
files used to create the manual with prefixes suited for the
new manual name, which is "Getting Started With Yocto Project".

The style sheet for the new manual needed updating to display the
new .PNG image for the title page.  The mega-manual file had to
be updated to include the files.  The mega-manual.sed file had
to be updated to include the new manual and not use the overview
manual.

(From yocto-docs rev: 6c7abf9192390121000f577d6c98f259d290d15d)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/sdk-manual/sdk-appendix-obtain.xml

@@ -327,7 +327,7 @@
                 <para>Following is an example command that extracts the root
                 filesystem from a previously built root filesystem image that
                 was downloaded from the
-                <ulink url='&YOCTO_DOCS_OVERVIEW_URL;#index-downloads'>Index of Releases</ulink>.
+                <ulink url='&YOCTO_DOCS_GS_URL;#index-downloads'>Index of Releases</ulink>.
                 This command extracts the root filesystem into the
                 <filename>core2-64-sato</filename> directory:
                 <literallayout class='monospaced'>

documentation/sdk-manual/sdk-extensible.xml

@@ -247,7 +247,7 @@
         <para>
             The <filename>devtool</filename> command line is organized
             similarly to
-            <ulink url='&YOCTO_DOCS_OVERVIEW_URL;#git'>Git</ulink> in that it
+            <ulink url='&YOCTO_DOCS_GS_URL;#git'>Git</ulink> in that it
             has a number of sub-commands for each function.
             You can run <filename>devtool --help</filename> to see all the
             commands.