Add prefill support for obsidian://ledger links

[StreliaPico]

Pull Request Description

This PR adds basic support for prefilled fields for the Obsidian Protocol handler.

Calling the uri will open the Add to Ledger modal with
A uri call may look like the following:
obsidian://ledger?amount=100&payee=Groceries

Supported fields:

• amount
• date
• payee
• toaccount
• fromaccount
• currency

Known Issues

• amount defaults to 0 instead of a blank field.
  • This is a typing issue. Changing the accepted type on the object class might solve this but possibly introduce issues elsewhere.
• currency, while it works, is not reflected in the UI which will show your Currency Symbol as selected in the settings.
  • Additionally, it successfully defaults to the selected currency despite not having been specified. Perhaps this implementation ought to be more explicit.
• Modal will fail to load if run while Obsidian is not already running.
  • This is already the case with the current codebase, and seems to already be documented in Ledger mobile shortcut only loading Obsidian  #78.