Indicate detection of failed PM module on display

[nick-4711]

It can happen that a PM module reports very (unrealistically) high _AE and _SP values. Here an example from the field

PM1_AE{1}: 3661.00
PM25_AE{1}: 3661.00 <--
PM10_AE{1}: 3661.00
PM1_SP{1}: 5492.33
PM25_SP{1}: 5492.33 <--
PM10_SP{1}: 5492.33
PM003_PC{1}: 396.33 <--
PM005_PC{1}: 232.67
PM01_PC{1}: 0.00
PM25_PC{1}: 0.00
PM05_PC{1}: 0.00
PM10_PC{1}: 0.00

normal would be something like

PM1_AE{1}: 27.00
PM25_AE{1}: 44.00 <--
PM10_AE{1}: 51.00
PM1_SP{1}: 32.00
PM25_SP{1}: 55.00 <--
PM10_SP{1}: 55.00
PM003_PC{1}: 521.00 <--
PM005_PC{1}: 478.00
PM01_PC{1}: 104.00
PM25_PC{1}: 10.00
PM05_PC{1}: 0.00
PM10_PC{1}: 0.00

Right now

• these values are dropped (and not transmitted to the backend)
• we display "-" on the OLED

With this issue we want to change this behavior and

• transmit the values to the backend to allow to feed this into fault detection algorithms (e.g. Felipe)
• discuss if we should also deliver such values on the local HTTP server interface or better drop them / or also indicate the failure somehow
• display "x"? or some other icon indicating failure if we see a value higher than 999?

Maybe we can then use this approach for all measures.