src: brightness: Fix LOG_BRIGHTNESS == 1

Various includes where missing, making the compilation with LOG_BRIGHTNESS
enabled fail.
src: Replace functions dealing with string conversions with <stdio.h> equivalents

This replaces all occurences of the custom string conversion function with the
printf() and scanf() function family. Although this takes up considerable
amount of space, it is more flexible and the advanced features of these
functions can come in handy in this project.
src: Implement module specifying format strings

This introduces a new module, which specifies various format strings and makes
them accessible througout the whole project. These strings are put into program
space once and can be re-used across different other modules.

On top of that this commit makes also sure that all of the existing printf()
invocations make use of this new facility.
src: Remove unused base includes
src: config.h: LOG_LDR2PWM: Add todo items
Merge branch 'feat/printf'
src: config.h: LOG_PREFERENCES_SAVE: Fix references to wrong file
src: Introduce new format strings and make use of them
src: format: Name format strings consistently
src: user.h: Remove name of struct
src: user.h: Rename UiTime to ui_time_t
src: Remove names of structs that are also type definitions
src: Remove names of enumerations that are also type definitions
src: user.c: Rename POWER_STATES enumeration to user_power_state_t and define it as type
src: user.c: Rename g_powerState to user_power_state
src: format.h: Add empty line between input and output formats
src: Make use of formats from format.h consistently

This makes sure that the format strings defined by the format module are used
throughout the project consistently.
src: usermodes.c: Check for LOG_USER_IR_TRAIN == 1
lib: IRMP: Bump version to 2.6.7
Merge branch 'feat/irmp'