Add some Certificate Authorities to trust store for AssetFetcher

[jisqyv]

Older versions of Android do not trust the Let's Encrypt Root. So we add it to the TrustManager for the connection we use in the AssetFetcher.

This code was cribded from ChatBot.java and put into its own class. At some point we should refactor ChatBot, Imagebot and CloudDB to use this new class.

Change-Id: Ifcc680295782b7aa6d04781c3230d026ae7af344

What does this PR accomplish?
Permits older devices to use sites protected by Let's Encrypt, whose root certificate is not in the trust store of older devices
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