OMB - Major Refactor (#39)

* OMB - Major Refactor

- Aliases and completions now works like plugins (need to enabled in .bashrc)
- Removed the compatible check in spectrum.sh, OMB now works with Bash v3.x like the old days.
- Removed core plugin, added those bash functions into base.sh and load during startup.
- Updated OSH template for new installations
- Added history config and few other stuff from #17

@TODO: Added a shell script to update old version of .bashrc to new one.

* Fixed ShellCheck issues

* Fixed ShellCheck issues

completions/nvm.completion.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+# nvm (Node Version Manager) completion
+
+if [ "$NVM_DIR" ] && [ -r "$NVM_DIR"/bash_completion ];
+then
+  . "$NVM_DIR"/bash_completion
+fi