feat: authentication mechanism for seed

[D-Nice]

Research (Both security implication-wise and end-user), if AES-GCM alone is sufficient as an auth guarantee for the seed phrase (that someone didn't maliciously change the seed phrase):

• [x] implement seed phrase encryption as AES256-GCM on user-end. - [ ] maybe add identicon for m/1337'/0' ( or other) acct - [ ] consider any other options, technically https://github.com/SrsSec/SrsPass-pwa/issues/4 should aid in authentication, in that they will fail to decrypt, if the seed phrase is changed. A warning can be emitted regarding this, indicating corruption of some sort.

blocked by https://github.com/SrsSec/SrsPass-pwa/issues/3 needing stores implementation first

[D-Nice]

2,3 will go to mvp 0.3 milestone in separate issue

[D-Nice]

closed by https://github.com/SrsSec/SrsPass-pwa/commit/159f297b8b0cf8e48cbc74126f0f7aa94426306b#diff-6f0eb39b514a42780ab1a59580bfdf290010ceebbce313c08125b16a741bbb85R95