Fix token transfer screen issues

Purpose

This PR fixes several issues with the token transfer screen (SendTokenActivity).

Fixed:

AmountEditText not allowing decimal input in locales with , decimal separator
AmountEditText limiting the input to fit into long
AmountEditText not allowing highly precise amount input due to the hardcoded 6 decimals
Overflow-caused crashes in amount validation logic
Unnecessary conversions and assignments in amount validation logic
"Max" button not showing the disabled state
"Max" button either doing nothing or setting the wrong amount when a non-CCD token is selected
Keeping the "Insufficient funds" error after switching the token
Showing an outdated fee estimate while the fresh one can't be loaded
Not working memo input
Not showing the memo on the receipt screen
Incorrect appearance of the "Insufficient funds" error after switching between CCD and tokens

Now, the "Max" button is always available when a non-CCD token is selected, regardless of whether the fee is loaded or not.

[x] My code follows the style of this project.
[x] The code compiles without warnings.
[x] I have performed a self-review of the changes.
[x] I have documented my code, in particular the intent of the hard-to-understand areas.
[x] (If necessary) I have updated the CHANGELOG.

_Remove if not applicable.

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