Implement button push using servo motors controlled via pwm (#55)

1. Add to /boot/config.txt
```
dtoverlay=pwm
```

2. Create /etc/udev/rules.d/99-kvmd-pwm.rules
```
SUBSYSTEM=="pwm*", ACTION=="add", RUN+="/bin/chgrp -R kvmd /sys%p", RUN+="/bin/chmod -R g=u /sys%p"
SUBSYSTEM=="pwm*", ACTION=="change", ENV{TRIGGER}!="none", RUN+="/bin/chgrp -R kvmd /sys%p", RUN+="/bin/chmod -R g=u /sys%p"
```

3. Connect Servo motor like SG90 PWM connection to RPi GPIO18, +5V and GND to a 5V and GND pin on header

4. Add to /etc/kvmd/override.yaml
```
kvmd:
    gpio:
        drivers:
            servo1:
                type: pwm
                pwm_chip: 0                  # PWM Chip Number
                pwm_period: 20000000         # Servo Motor SG90 Period in nano-seconds
                duty_cycle_push: 1500000     # Servo Motor SG90 duty_cycle for pushing button
                duty_cycle_release: 1000000  # Servo Motor SG90 duty_cycle for releasing button
        scheme:
            short_press:
                driver: servo1
                pin: 0                       # Pin number is the PWM channel number on the PWM Chip
                mode: output
                switch: false
                pulse:
                    delay: 0.5
                    max_delay: 2
            long_press:
                driver: servo1
                pin: 0                       # Pin number is the PWM channel number on the PWM Chip
                mode: output
                switch: false
                pulse:
                    delay: 2
                    max_delay: 2
            extra_long_press:
                driver: servo1
                pin: 0                       # Pin number is the PWM channel number on the PWM Chip
                mode: output
                switch: false
                pulse:
                    delay: 10
                    max_delay: 20
        view:
            header:
                title: Controls
            table:
                - ["#Servo - Short Press", "short_press|Press"]
                - ["#Servo - Long Press", "long_press|Press"]
                - ["#Servo - Extra Long Press", "extra_long_press|Press"]
```

1 files changed, 1 insertions, 0 deletions

diff --git a/testenv/Dockerfile b/testenv/Dockerfile
index 5e8b2a79..0f3d3bfd 100644
--- a/testenv/Dockerfile
+++ b/testenv/Dockerfile
@@ -23,6 +23,7 @@ RUN pacman -Syu --noconfirm \
 		python-yaml \
 		python-aiohttp \
 		python-aiofiles \
+		python-periphery \
 		python-passlib \
 		python-pyserial \
 		python-setproctitle \