Improvements to outdated filesystem prompt

[jeffgca]

Summary

The filesystem prompt could be improved:

1. This is the text the use gets:

Your filesystem is outdated.

Please upgrade your filesystem by running a miration (https://guide.fission.codes/accounts/account-signup/account-migration) or click on "remove this device" and create a new account.

(Filesystem version: 1.0.0. Webnative version: 0.30.0-alpha15)

1. miration -> migration

2. Consider moving the entire message to an in-content prompt so that links can be used. As it stands using an alaert dialogue forces the user to manually not down the link to the account migration guide.