Blocking number suppresses voicemails in the same minute

~ Modified FilteredNumbersUtil to check if a voicemail needs to be
blocked by checking if the voicemail date matches the block date to
the minute, rather than millisecond
~ Modified FilteredNumbersUtil#shouldBlockVoicemail to improve
readability

+ Added tests to verify FilteredNumbersUtil#shouldBlockVoicemail

Bug: 25346075
Change-Id: I9851a574f0d13b7f09c99438810454770c88aa8b