emissary-171: addressed most easily remedied CodeQL security findings

[drivenflywheel]

Address CodeQL security findings. (Partially) addresses #171

[drivenflywheel]

This commit addresses the following 10 alerts:

• Implicit narrowing conversion in compound assignment (src/test/java/emissary/pickup/FTestFailedPickupClient.java#L163)
• Information exposure through a stack trace (src/main/java/emissary/server/api/Pause.java#L25)
• Information exposure through a stack trace (src/main/java/emissary/server/api/Pause.java#L32)
• Information exposure through a stack trace (src/main/java/emissary/server/api/Shutdown.java#L41)
• Information exposure through a stack trace (src/main/java/emissary/server/mvc/TransferDirectoryAction.java#L47)
• Information exposure through a stack trace (src/main/java/emissary/server/mvc/internal/WorkSpaceClientSpaceTakeAction.java#L51)
• Cross-site scripting (src/main/java/emissary/server/mvc/TransferDirectoryAction.java#L43)
• Cross-site scripting (src/main/java/emissary/server/mvc/internal/RegisterPeerAction.java#L49)
• Cross-site scripting (src/main/java/emissary/server/mvc/internal/RegisterPeerAction.java#L52)
• Cross-site scripting (src/main/java/emissary/server/mvc/internal/WorkSpaceClientSpaceTakeAction.java#L44)

Second commit resolves the following alert:

• Uncontrolled data used in path expression (src/main/java/emissary/output/DropOffUtil.java#L315)

[drivenflywheel]

Verified that there were no references to this overload in downstream repositories.