Add emoji support

- `:hammer:` should render 🔨 in the web app.
- Ensure that existing emoji support doesn't change.
- This change will have to be made when the commit message has been read, so before returning from [`getCommitMsg()` in `generateObjects.js`](https://github.com/HarshKapadia2/git-graph/blob/062e9f344baaff1f3cb373344094f0eb19aea306/src/util/generateObjects.js#L169).
- One way to implement this would be to check for the indices of all the colons (`:`) and then try to extract the text between two colons to check if it matches an emoji text.

Current behaviour:

Expected behaviour:
- `:sparkles:` should render as ✨ in the commit message.
- `:truck:` should render as 🚚 in the commit message.

_Originally posted by @HarshKapadia2 in https://github.com/HarshKapadia2/git-graph/discussions/40#discussioncomment-3225894_