Improved pear dependency installation to use config file when present.

PEAR packages can now be managed using a config file, al-a composer,npm, etc.

Create a file at `Config/pear_packages.txt` with one `[channel:]package` pair per line, like so:

```text
PHP_CodeSniffer
pear.cakephp.org:cakephp/CakePHP_CodeSniffer
pear.survivethedeepend.com:deepend/Mockery
hamcrest.googlecode.com/svn/pear:deepend/Mockery
```

The first line is an example of a package available from the default channel (pear.php.net). The last two lines indicate how to install additional channels that don't have a specific package related to them (supply a duplicate package name).

Use `pear-install-deps` without arguments to install/update channels and packages from the new config file. The script works around a huge number of janky problems surrounding PEAR and makes them somewhat automate-able.

It is included in the new `deps-install` (which in turn is now used in `update`), which detects the executables and associated config files for:

* PEAR
* composer
* npm

...and runs install commands for those that are present. _(Having a config present but the binary missing throws an error. If you aren't using one of these dep managers but have a config file in place: Either remove the config file or install the binary!)_