Extract UI related config params into a UIConfig type

[saurabhnanda]

Problem

1. Config{..} type was mixing up config params required for the job-runner along with the config params required for the web-UI.
2. There are cases where we want to start job-runners independently of the web-ui (typically you will only have one instance of the web-ui, whereas you may have multiple instances of the job-runner on different machines)
3. The mixing-up of these two concerns in the Config{..} type forces one to define unnecessary config params if only the web-ui needs to be started or only the job-runner needs to be started

Sub-problem

• The callback-within-callback style of OddJobs.Cli is very confusing. It was confusing even for me when I wanted to write a custom CLI for some purpose.

Solution

1. Introduced Types.UIConfig{..}
2. Introduced Cli.CliType that allows one to easily start only the job-runner, only the web-ui, or both.
3. OddJobs.Cli parses the command-line and builds a Config -> Config (or UIConfig -> UIConfig) function that overrides the default config based on command-line arguments. This function can be passed to mkConfig or mkUIConfig. This avoid the "callback-withing-callback" style to some extent.

[saurabhnanda]

@tfausak @kanagarajkm @jappeace @ivb-supercede @leomayleomay @mrputty @aschmois this is a moderately large breaking change. Please share your thoughts about this.

[tfausak]

I haven't looked at the changes too closely, but it all sounds good to me and we should be able to adapt to these changes.

[kanagarajkm]

@saurabhnanda we don't use the webui and don't fiddle with any config. changes should be fine for us.

[ivb-supercede]

Sounds good to me.