Modbus web configuration: add check for valid delay and period parameters

IDE: Fix missing highlighted element in diagrams when using GTK3

- wx's logical function does not work on gtk3, and highlighting relies on it
- skipping logical funciion at all "works" but this now makes highlight opaque
- no easy fix for highlight transparency since emulated with AND Wx logical function
+ added other highlight related cosmetic fix.

Merged default in wxPython4 branch

Linux runtime: overrun detection for real-time timers and for plc execution.

If real-time timer wakes-up PLC thread too late (10% over period), then
warning is logged.

If PLC code (IO retreive, execution, IO publish) takes longer than requested
PLC execution cycle, then warning is logged, and CPU hoogging is mitigated
by delaying next PLC execution a few cylces more until having at least
1ms minimal idle time.

Fix typo in toolchain_gcc.py : LDLAGS -> LDFLAGS

Merged from default

Merge.

SVGHMI: add two more simple widgets to default widget library

Cosmetic fix in plc_debug.c template

Merge.

Modbus plugin: add optional delay between two consecutive modbus requests sent by master/client

Runtime: Add RealTime checkbox in Linux target options to enable PREEMPT_RT scheduling.

Runtime: move LC_NUMERIC locale setting to Beremiz_service.py.

Test: Customize Fluxbox launch to get rid of toolbar in IDE tests.

Tests: Use TESSERACT_LSTM_COMBINED, LSTM + Legacy OCR mode in Sikuli, more stable results.

Merged default in wxPython4 branch

Runtime: Fix bugs in Linux target.

- next occurence absolute time computation failing on 32-bit because of casting
- PLC thread was started before period was set, potentially passing uninitialized timespec to clock_nanosleep()

runtime: Change Linux target to use clock_nanosleep instead of timer (better rt-preempt perf).

Linux runtime: fix thread waiting on wait_RT_to_nRT_signal not being waken-up when delete_RT_to_nRT_signal is invoked.

Tests: docker image needs tesseract4, but opencv lib since sikuli.jar already contains it.

More explicit default value for generic makefile target command. Assume Makfile is located in project_files

IDE: prevent IDE/CLI process surviving to sys.exit() by using deamon threads to monitor external processes output streams.

Tests: allow overriding local host's hostname with BEREIS_LOCAL_HOST env variable.

Tests: IDE: explicitely wait for build success rather than just stdout to become silent.

Tests: Fixed wrong path (relative to $HOME) in CLI tests.

Tests: OPCUA tests can now use OPCUA_DEFAULT_HOST environment variable to force host to something else than "127.0.0.1" or "localhost"

IDE: fix segfault when unselecting network discovery in URI editor

IDE: fix exception when showing project's context menu in case of empty clipboard (wxpython4).

Tests: Fix dockerfile not finding locales.

cosmetic fix