Grey out Source when sending

[Stoner19]

Mojo wallet prevents users from using the Source address as the change address when sending, so in order to prevent the error, I propose that the Source address is greyed out so the user is unable to select it as a change address.

Error as shown:

java.lang.IllegalArgumentException: Change address must be different than source address
org.ortis.mochimo.mojo.core.wallet.Wallet.sign(Wallet.java:768)
org.ortis.mochimo.mojo.app.wallet.WalletEntryModelImpl.sign(WalletEntryModelImpl.java:80)
org.ortis.mochimo.mojo.gui.swing.tasks.SpendTask.task(SpendTask.java:110)
org.ortis.mochimo.mojo.gui.swing.tasks.AbstractGUITask.run(AbstractGUITask.java:49)
java.lang.Thread.run(Thread.java:748)

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Parsing payment amount
Signing transaction