Add runtime configuration for disabling BatteryChargingFlag led pattern

Makes runtime control possible and stops mce from complaining at startup.
Do not complain if optional mce-plugin-libhybris is not installed

Still emits diagnostic message if mce was started in verbose mode.
Add functions for checking availability of config groups/keys

When dealing with optional items, these can be used to avoid implicit
error logging from group/key get functions.
No complaints from missing optional CPUScalingGovernor config items

As it is normal that Interactive/Default configuration is missing,
no diagnostic output should be emitted on normal verbosity level.
Use valid initial value for cached high brightness level

The initial value can get used as such and thus it must be valid.
Use environment as substitute for product id sysinfo value

When mce is started normally via systemd, at least N9 and N950 can be
detected from product_name environment variable. This information is
needed when setting up indication led/keyboard backlight functionality.

To ease running mce manually for debugging purposes, the environment
values from /proc/1/environ are used as secondary source of information.
No complaints from missing optional color profile config items

As it is normal that display color profile configuration is missing,
no diagnostic output should be emitted on normal verbosity level.
No complaints from missing optional boot status directory

As the use of /run/systemd/boot-status directory and init-done flag
file is optional, no diagnostic output should be emitted on normal
verbosity level if they are not present.
Silence missing calibration data complaints while sysinfo is disabled

While the calibration data can't really be read, it makes little sense
to emit diagnostic messages about the failures on normal verbosity level.
Add missing hybris led patterns configurations

The config needs to be revisited later, these are just placeholders.
Remove accidentally left in debug logging
Omit warning if radio state files are not present

If the reading fails, mce will try to generate the radio state
files with default content and any problems with missing directories
etc will be caught there.
Merge pull request #62 from spiiroin/misc_warnings

Cleanup warnings that occur on mce startup