templates: Change templates to use ZIM_HOME

According to ZSH documentation (http://zsh.sourceforge.net/Doc/Release/Files.html),
~/.zshrc is sourced before ~/.zlogin, so defining ZIM_HOME in zshrc
and using in zlogin should work.

templates/zlogin

@@ -17,7 +17,7 @@
     fi
   }
 
-  zim_mods=${ZDOTDIR:-${HOME}}/.zim/modules
+  zim_mods=${ZIM_HOME}/modules
   setopt EXTENDED_GLOB
 
   # zcompile the completion cache; siginificant speedup.

templates/zshrc

@@ -4,8 +4,11 @@
 # User configuration sourced by interactive shells
 #
 
+# Change default zim location 
+export ZIM_HOME=${ZDOTDIR:-${HOME}}/.zim
+
 # Source zim
-if [[ -s ${ZDOTDIR:-${HOME}}/.zim/init.zsh ]]; then
-  source ${ZDOTDIR:-${HOME}}/.zim/init.zsh
+if [[ -s ${ZIM_HOME}/init.zsh ]]; then
+  source ${ZIM_HOME}/init.zsh
 fi