Remove Oh-My-Fish & Use Sashimi Prompt

- Remove oh-my-fish
- Update fish dracula theme
- Add sashimi fish prompt directly to config file
- Modify default sashimi colors to use dracula colors
- Move greeting and prompt to main config file

.gitmodules

@@ -10,6 +10,3 @@
 [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