Add help stubs

initial commit of basic seahorse task stubs. linking not yet established.
Update application name in help
docs: added seahorse icon and modified the index page to include the icon.
docs: added page about certs. initial draft of ssh-key description.
docs: added draft to explain public vs private keys.
added draft page on how to create a pgp key.
docs: updated index page. cleaned up key creation pages. added simple page to summarize adding keys.
docs: updated index page. cleaned up key creation pages. added simple page to summarize adding keys.
docs: added group and groups information to learning sections. reworked what-diff-priv-public page
docs: refactored the landing page, moving general info about keys to a separate sub-page.
docs: fixed validation error on learn-about-keys.page
help: Comment on some of the 'learning' pages

Hopefully this commit will be squashed when me merge this branch.
But we can worry about that later.
Added a list of basic terms in introduction.page

Explanation of some technical terms involved.
Updated user help: introduction.page

Corrected <p> indents.
Added the term "Algorithm" to the list.
Updated help: Added draft: encryption-rsa.page

Added the first draft for encryption-rsa.page.
Page might have to be changed if some concepts are too
mathematical.
Updated help: encryption-rsa.page

Edited <include> tag to include pkgversion
Update help: key-servers-what-are-they.page

Aded information to the skeleton.
Reflowed text.
Updated help: New page stubs

Added new page stubs for explaining how to sync and publish
public keys and retrieve remote public keys.
Update help: encryption-rsa.page

Minor edits to the page.
Updated help: key-signing-event.page

Renamed page as key-signing.page.
Explained why key signing is necessary.