flavours: Check for nvim plugin existence in template

Checks that mini.base16 plugin exists before executing its setup,
and checks that lualine exists before executing its setup.

desktop/.config/flavours/templates/nvim/templates/default.mustache

@@ -7,6 +7,13 @@
 -- by RRethy (https://github.com/RRethy/nvim-base16)
 -- {{scheme-name}} scheme by {{scheme-author}}
 
+local function exists(plugin)
+    local status, lib = pcall(require, plugin)
+    if(status) then return true end
+    return false
+end
+
+if exists("mini.base16") then
     require('mini.base16').setup({
         palette = {
             base00 = '#{{base00-hex}}',
@@ -27,6 +34,9 @@ require('mini.base16').setup({
             base0F = '#{{base0F-hex}}'
             },
     })
-require('lualine').setup()
+end
+if exists("lualine") then
+    require("lualine").setup()
+end
 
 -- vim: filetype=lua