Oh My Fish & bobthefish Theme

- Add oh-my-fish repo as submodule
- Remove powerline shell from fish
- Move fish greeting from config.fish to fish_greeting.fish function
- Add bobthefish configuration to config.fish

.gitmodules

@@ -10,3 +10,6 @@
 [submodule ".config/slstatus"]
 	path = .config/slstatus
 	url = https://github.com/balajsra/slstatus.git
+[submodule ".config/oh-my-fish"]
+	path = .config/oh-my-fish
+	url = git@github.com:oh-my-fish/oh-my-fish.git