Add Lualine theme

[Nandax00]

Looks as follows:

• Normal mode:
• Insert mode:
• Visual mode:
• Command mode:
• Replace mode:

I have used the following Lualine config:

require("lualine").setup {
    sections = {
        lualine_b = { "diagnostics" },
        lualine_c = {
            {
                "filename",
                newfile_status = true,
                path = 1, -- relative path
                symbols = { modified = " ●" },
            }
        },
    },
    tabline = {
        lualine_a = {
            {
                "tabs",
                mode = 2, -- tabnumber + filename
                use_mode_colors = true,
                symbols = { modified = " ●" },
            }
        },
        lualine_b = { "branch", "diff" },
    },
}

closes #61.

[Nandax00]

Applied suggestions from #85.