[FEATURE] - Themeable Templates

[SarthakT7]

User should be able to provide a theme for the templates

User chooses a color from the colorpicker and they are able to generate an invoice with that theme color.

Use Case

Especially benifical when an organization/business wants to apply their branding.

Proposed Solution

We shall discuss with the maintainers if they have some philosophy behind theming. If we have some references/designs that we want to live up to, we can implement it.

Additional Information

I need some understanding regarding what sections of the invoice we want to theme. I can work on this feature