* Set a timeout for `isValidTimeout`

When using ssh with db connections:
Our theory is that the db connection has no idea that it sits on top of
an ssh connection. And if the ssh connection dies (ie, `show full
processlist` and then `kill <id>` from that list in mysql) the db
connection has no idea it is dead. "It" is valid but its ssh transport
is dead.

> It is possible to customize how c3p0's DefaultConnectionTester tests
> when no preferredTestQuery or automaticTestTable are available. Please
> see Configuring DefaultConnectionTester.isValidTimeout and Configuring
> DefaultConnectionTester.QuerylessTestRunner.

from https://www.mchange.com/projects/c3p0/#automaticTestTable

> Configuring DefaultConnectionTester.isValidTimeout

> Under circumstances when the JDBC 4+ isValid(...) test will be used by
> c3p0's built in DefaultConnectionTester (see below), by default the test
> will never time out. If you would the test to timeout and fail, set the
> following key

>    com.mchange.v2.c3p0.impl.DefaultConnectionTester.isValidTimeout

> to the desired timeout, in seconds.

https://www.mchange.com/projects/c3p0/#configuring_dctivt

* Bump to 6 seconds. Worried 3 might be a bit too quick

As per configuration_precedence document noted in the c3p0 config doc
(https://www.mchange.com/projects/c3p0/#configuration_precedence) any
setting which is specified programatically may not be overridden by
other external settings such as system properties.  This creates an
issue if an admin wishes to set any of these settings.

In my case I was attempting to have c3p0 shut down all connections
to my RDS instance so that amazon would spin the instance down while
not in use.  Alas it appears that something else seems to re-establish
connectinons every few seconds and prevent my desired behavior. But
before I abondon this approach I figured this would be a good PR
for the project as it will enable others to set this settings as they
see fit and not hit the same roadblocks I hit along the way.

Of note I have removed the maxPoolSize setting as the current value
of 15 is the same as the driver default. The other settings remain.

move /frontend_client -> /resources/frontend_client to make sure the static resources are bundled in our jar files.
small updates to main routes.clj file to make static asset serving from "resources" instead of "files", which allows for serving out of jars.