First, VS2015 doesn't appear to support importing alias templates directly,
so let's make an alias template ourselves and import every alias we need.
That approach doesn't work with VS2013, apparently due to lack of support
for expression SFINAE. Thus, we now use our custom alias templates on
VS2013.
Also, I moved type_trait_aliases.hpp to the wesnothlib project where it
belongs.
Note that because of requiring expression SFINAE on VS2015, building
Wesnoth on VS2015 now requires that Update 1 or above is installed.
This also removes the included SHA1 and MD5 implementations
in favour of those from OpenSSL.
Thanks to @jyrkive for helping to get the CMake build working and
ensuring the game still compiles with OpenSSL 1.1.0.
(The SHA_xxx() aliases were removed in OpenSSL 1.1.0.)
The game now supports @ or = in usernames for the purpose of saving them to a file.
Though I don't think these are allowed currently, it's probably better to
support it from the start rather than having things break if they later
become allowed.
Looking at this more I realized the help_button was a GUI1 dialog component meant to open the Help
dialog. Since all dialogs invoking Help now use GUI2, there's no need for this class anymore. It
also allows a bunch of remaining GUI1 stuff to be cleaned up.
This was a dialog used early in 1.13 during the SP/MP codepath unification to configure certain options.
The modification selection is now built into the Selection dialog, and we decided not to enable other options
like Era selection in SP. The only option we might look to restoring in the future is the "show_connect"
option, but that requires some additional code elsewhere and probably won't be used anyway.
I left the controller passed in an argument for compatibility with the GUI1 dialog, but since that's removed
it makes sense that the dialog handle the creation of the controller, especially since due to an oversight
it made a copy instead of holding a reference.
This also allows storyscreen/interface.*pp to be removed. The START_POSITION was part of the GUI1 implementation
and isn't needed anymore.
