Move sample_prompts/themes to share/

They are used by "fish_config" CLI too, so no need to make them
private to webconfig.  Putting them at top-level seems simpler overall.

share/prompts/pythonista.fish

@@ -0,0 +1,29 @@
+# name: Simple Pythonista
+# author: davbo
+
+function fish_prompt
+    if not set -q VIRTUAL_ENV_DISABLE_PROMPT
+        set -g VIRTUAL_ENV_DISABLE_PROMPT true
+    end
+    set_color yellow
+    printf '%s' $USER
+    set_color normal
+    printf ' at '
+
+    set_color magenta
+    echo -n (prompt_hostname)
+    set_color normal
+    printf ' in '
+
+    set_color $fish_color_cwd
+    printf '%s' (prompt_pwd)
+    set_color normal
+
+    # Line 2
+    echo
+    if test -n "$VIRTUAL_ENV"
+        printf "(%s) " (set_color blue)(path basename $VIRTUAL_ENV)(set_color normal)
+    end
+    printf '↪ '
+    set_color normal
+end