Feat: Implement a default theme

[hermitmaster]

It would be great if this worked:

use {
    'goolord/alpha-nvim',
    requires = { 'kyazdani42/nvim-web-devicons' },
    config = function ()
        require'alpha'.setup {}
    end
}

I would default to Startify, as it doesn't depend on specific plugins or keycaps and it just works out of the box.