Add support for concurrency limit

Currently there is support for the following limits for a function:

```
const (
// supported
LIMIT_VALUE_TIMEOUT = "timeout"
LIMIT_VALUE_MEMORY_SIZE = "memorySize"
LIMIT_VALUE_LOG_SIZE = "logSize"
// unsupported
LIMIT_VALUE_CONCURRENT_ACTIVATIONS = "concurrentActivations"
LIMIT_VALUE_USER_INVOCATION_RATE = "userInvocationRate"
LIMIT_VALUE_CODE_SIZE = "codeSize"
LIMIT_VALUE_PARAMETER_SIZE = "parameterSize"
)
```

`concurrency` is a limit that can be manually applied to a function using the wsk CLI, but can't be applied to functions in a wskdeploy manifest.yaml. it is **different** than `concurrentActivations`

ie: `wsk action update --concurrency 100 `

It is used to allow a number of functions to be run concurrently in the same container determined by the concurrency number.

Start by tracing how wskdeploy reads limits from manifest.yaml and how the existing timeout, memorySize, and logSize limits are handled. Compare that path with the stated wsk CLI --concurrency behavior; done means a manifest can specify concurrency and deployment applies it distinctly from concurrentActivations.

Written by the indexing model from the issue text.