Add a menu with links to the sites for previous years

[alastairs]

The build log indicates the failure is:

[19:21:12][Step 1/1]        "C:\TeamCity\buildAgent\work\77c9f48fc195cd03\DDDEastAnglia.sln" (Build target) (1) ->
[19:21:12][Step 1/1]        "C:\TeamCity\buildAgent\work\77c9f48fc195cd03\DDDEastAnglia\DDDEastAnglia.csproj" (default target) (2) ->
[19:21:12][Step 1/1]        (CoreCompile target) -> 
[19:21:12][Step 1/1]          Controllers\GravatarController.cs(8,30): warning CS0108: 'DDDEastAnglia.Controllers.GravatarController.Url(string, bool, int)' hides inherited member 'System.Web.Mvc.Controller.Url'. Use the new keyword if hiding was intended. [C:\TeamCity\buildAgent\work\77c9f48fc195cd03\DDDEastAnglia\DDDEastAnglia.csproj]
[19:21:12][Step 1/1] 
[19:21:12][Step 1/1] 
[19:21:12][Step 1/1]        "C:\TeamCity\buildAgent\work\77c9f48fc195cd03\DDDEastAnglia.sln" (Build target) (1) ->
[19:21:12][Step 1/1]        "C:\TeamCity\buildAgent\work\77c9f48fc195cd03\DDDEastAnglia.Tests\DDDEastAnglia.Tests.csproj" (default target) (4) ->
[19:21:12][Step 1/1]        (CoreCompile target) -> 
[19:21:12][Step 1/1]          ConferenceLoaderBuilder.cs(61,40): error CS0161: 'DDDEastAnglia.Tests.ConferenceLoaderBuilder.WithTotalNumberOfSessions(int)': not all code paths return a value [C:\TeamCity\buildAgent\work\77c9f48fc195cd03\DDDEastAnglia.Tests\DDDEastAnglia.Tests.csproj]
[19:21:12][Step 1/1] 
[19:21:12][Step 1/1]     1 Warning(s)
[19:21:12][Step 1/1]     1 Error(s)

[adrianbanks]

Re: build failure. This was due to a broken merge on production. I've fixed that separately.