Add a default vault feature by adding 2 environment variables. Currently usage by on (add new note) command.

[sanchitsharma]

Addressing Issue #35

1. introduce two new variables - defaultVaultPath and defaultVaultName
2. add a new input "oadddefaultvault" to change/add the default vault name and path.
3. on addition of first new vault, it is automatically made the default vault as well (it can be changed via above input anytime later)
4. current "on" keyword is remapped to "onv" (v=vault)
5. "on" is now used to add directly to add to the default vault (Vault name shown in title by showing "Creating {query} in {defaultVaultName})"
6. In clearvaults flow, reset default vault value as well

Once we agree on the flow, or I have done any other required changes, I can edit the PR to add documentation and demo as well in README.

[hauselin]

Thanks for the PR! I'll take a look in the next few days!