remove unnecessary parse() code that throws a NPE

closes #3742 https://dev.guardianproject.info/issues/3742
simplify SerializedSecretsV1 interface to just what is needed and used

The only operations that SerializedSecretsV1 needs to provide is setting up
and instance in the constructor, then getting the info encoded in a byte
array.

refs #3742 https://dev.guardianproject.info/issues/3742
move notification icon to sample project

This puts the lib one step closer to only being a jar!

refs #3680 https://dev.guardianproject.info/issues/3680
purge CacheWordActivityHandler, its a pointless wrapper of CacheWordHandler

Instead, apps should just instantiate CacheWordHandler and call
connectToService() and disconnectFromService() where appropriate.  That is
most likely going to be in an Activity's onResume() and onPause()
respectively.
move getApplicationContext() into getBlankServiceIntent()

Since CacheWordService.getBlankServiceIntent() requires a long-lived
Context, move the call to getApplicationContext() into the method itself to
guarantee that it gets the Application's Context.
purge built-in Notification, the app must now provide it

Previously, there was an elaborate, custom framework for customizing the
Notification that was hard-coded into CacheWord.  Now, the app must supply
a Notification, and that triggers CacheWordService to run as a foreground
Service.  Otherwise, CacheWordService will run as a background Service with
no Notification.

This removes the last remnants that require CacheWord to be an Android
Library Project.  Now it can be distributed as just a jar.  It can still be
used as a Library Project for those who like doing it that way.

fixes #3711 https://dev.guardianproject.info/issues/3711
fixes #3680 https://dev.guardianproject.info/issues/3680
improve javadoc comments on CacheWordHandler

CacheWordHandler is the main interface, so it should be well documented.
rename CacheWordHandler.lock() to match CacheWordHandler.isLocked()

Clean up some unneeded redirection while we are at it.  If it is ever
needed in the future, it can be easily added back in.
rename INTENT_PASS_EXPIRED to INTENT_LOCK_CACHEWORD

This Intent causes CacheWord to lock, so this name makes more sense.
purge CacheWordSettings and directly set timeout in CacheWordHandler

This removes the now pointless CacheWordSettings and provides options for
directly setting the timeout in seconds.  This changes the meaning of the
non-positive values:

>0 = timeout in seconds
 0 = disable timeout
<0 = use default value

fixes #3718 https://dev.guardianproject.info/issues/3718
move getBlankServiceIntent() to CacheWordHandler to unify interface

This means that basically everything that the developer will ever need to
do can happen using CacheWordHandler.
replace duplicate code with call to getPasswordLockPendingIntent()