Introduce AddWalletButton and connect it to the AddWallet flow

[johnny9]

These commits enable the "Add Wallet" button at the bottom of the Wallet Select menu on Desktop

[MarnixCroes]

4b79351
the space between the icon and the text is different than from master

Master

PR

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maybe for follow up:
At the AddWallet page, the Skip button in in the right top should get a condition to only have it when in the onboarding flow. Now in the app when you click add wallet button -> Add Wallet page has a skip button, which makes no sense. a cancel would be more appropriate

[hebasto]

cc @GBKS

[GBKS]

Nice work adding this functionality. I did a review of the full flow (MacOS) and added my notes in the visual below. Some of them will not be relevant to the focus of this PR and should probably be better handled in a separate one. Let me know how you want to handle that.

And in written form:

1. Wallet selector dropdown
1.1 All font sizes should be 15px (not 13, 14, and 15)
1.2 Reduce spacing between "+" icon and label in the "+ Add Wallet" button

2. Add a wallet screen
2.1 In the transition to this screen, the new screen should slide in from below (not from the right)
2.2 Replace "Skip" button in the top-right, but a "Cancel" button in the top-left (keep "Skip" on this screen when it is shown in the onboarding sequence)

3. Choose a wallet name screen
3.1 Replace "Continue" button label with "Next"

4. Choose a password screen
All good

5. Your wallet has been created screen
5.1 Do we want to offer a "Back" button here? It is convenient for users, yet also creates a new wallet every time they go back and forth - is that a problem?

6. Back up your wallet screen
6.1 Same question about the "Back" button as above
6.2 "View file" button label should be white
6.3 Reduce spacing between buttons to 20px
6.4 When exiting this screen, it should slide down

7. Activity screen post wallet creation
7.1 The newly created wallet should now be active

[rabbitholiness]

On macOS, the wallet name screen would not allow me to add spaces to the wallet name

[jarolrod]

This should be rebased over #427

[pablomartin4btc]

tACK 694025a

@rabbitholiness, this is only the UI link to the existent flow (CreateName.qml - not included in this PR), where there's a validator (dev's note: regexp qt class is deprecated and needs to be updated) which needs to be modified to include spaces as you said and I tested it too. Also to that flow we need to add functionality to the "Import wallet" and "View file" buttons, make the encryption not mandatory and perhaps as in Qt switch to the recently created wallet.

[MarnixCroes]

tACK 694025a