Improve mbed-tools --help text

**Describe the bug**
The help text for `mbed-tools` looks bad because Click truncates the short help text:
```
configure Generate an Mbed OS config CMake file and write it to a...
deploy Checks out Mbed program library dependencies at the revision...
```

Some of the information is also incorrect:
```
Options:
--version Display versions of all Mbed Tools packages.
```
We no longer have multiple mbed-tools packages so this text needs to change.

We also have a combination of imperative and indicative mood in the short help:
```
import Clone an Mbed project and library dependencies.
new Creates a new Mbed project at the specified path.
```
We should prefer imperative mood. So in the above example "Creates ..." should be "Create ...".

**To Reproduce**
Steps to reproduce the behavior:
`mbed-tools --help`

**Expected behavior**
Short help text is short enough so Click doesn't truncate it.
Help text information is correct and up-to-date with the current state of the tool.
Command descriptions use imperative mood.

Start by running `mbed-tools --help` and locate the CLI command definitions that provide the displayed short help and `--version` option text. Update the descriptions so Click does not truncate them, the version wording is current, and command descriptions use imperative mood; rerun `mbed-tools --help` to verify the output.

Written by the indexing model from the issue text.