[feature request] version checking

### Proposal:

On startup, if connection to the configured Telegraf or InfluxDB fails, check for a version mismatch rather than reporting a potentially cryptic error.
### Current behavior:

If there's an incompatibility between Kapacitor and another TICK component the error message may be cryptic or not even logged until a particular action is attempted and fails.
### Desired behavior:

On startup, Kapacitor detects it is connected to an older, potentially incompatible database and issues a warning in the logs. Potentially if the mismatch is very great, Kapacitor exits with the error.
### Use case:

Makes version mismatch issues much easier to diagnose and saves time and confusion.

The issue names no files, tests, or entry points. Start by tracing Kapacitor's startup connection handling for the configured Telegraf or InfluxDB services. Done means detecting an incompatible version, logging a warning, and defining when a severe mismatch should stop startup.

Written by the indexing model from the issue text.