Added support for custom title, logo, additional footer message.

Summary of Change
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Many companies have multiple Git servers - it's helpful to be able to differentiate them by name and logo.  Companies and individuals also need a spot to declare a copyright on the repository content (i.e. the code being stored), and also for a confidentiality message - this can now be set in the footer (without removing the current message).  This could be done in the Resources files, but those deploying the solution may not be coders, so having a spot to set these without updating an embedded resource is very helpful.

Summary of Alterations
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* Added three new user configuration settings: Site Title, Site Logo Url, and Site Footer Message
* Added fields on the settings page to support them.  Blanks are allowed and are the default, in which case current values (i.e. those before this change) are used.
* Updates made to the various cshtml files to include the new settings
* UserConfiguration, SettingsModels, SettingsController updated to manage editing and saving the settings.