Make `default` theme the default theme for omf.

* On clean install, configure and download `default` theme.
* Do not allow `default` theme to be removed.
* When the current theme is removed, fallback to `default`.

bin/install

@@ -99,8 +99,8 @@ omf_install() {
   if [ ! -d "${OMF_CONFIG}" ]; then
     echo "Writing Oh My Fish configuration → ${OMF_CONFIG}"
     mkdir -p "${OMF_CONFIG}"
-    touch "${OMF_CONFIG}/theme"
-    touch "${OMF_CONFIG}/bundle"
+    test -f "${OMF_CONFIG}/bundle"    || echo "theme default" > "${OMF_CONFIG}/bundle"
+    test -f "${OMF_CONFIG}/theme"     || echo default > "${OMF_CONFIG}/theme"
     test -f "${OMF_CONFIG}/revision"  || echo ${git_rev} > "${OMF_CONFIG}/revision"
   else
     fish -c "omf install"

pkg/omf/cli/omf.remove_package.fish

@@ -27,8 +27,8 @@ function omf.remove_package
     set -l remove_status 1
 
     if not omf.util_valid_package $pkg
-      if test $pkg = "omf"
-        echo (omf::err)"You can't remove `omf`"(omf::off) 1^&2
+      if test $pkg = "omf" -o $pkg = "default"
+        echo (omf::err)"You can't remove `$pkg`"(omf::off) 1^&2
       else
         echo (omf::err)"$pkg is not a valid package/theme name"(omf::off) 1^&2
       end
@@ -49,7 +49,7 @@ function omf.remove_package
       not test -d $path; and continue
 
       if test $pkg = (cat $OMF_CONFIG/theme)
-        echo "" > $OMF_CONFIG/theme
+        echo default > $OMF_CONFIG/theme
       end
 
       _remove_from_bundle "theme" $pkg

pkg/omf/util/omf.util_valid_package.fish

 function omf.util_valid_package -a package
   test (echo "$package" | tr "[:upper:]" "[:lower:]") = "omf"; and return 10
+  test (echo "$package" | tr "[:upper:]" "[:lower:]") = "default"; and return 10
   switch $package
     case {a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z}\*
       switch $package