[STM32xxx] CoIDE exporter and gcc_arm

- CoIDE options: wrap main and linker option DiscradUnusedSection=1 was
missing in some targets
- CoIDE options: corrected flash loader config for Nucleo_F030 and
Nucleo_F072
- CoIDE options: corrected memory layout (not used per default but now
it is the same as in linker script)
- gcc linker script: changed the memory size from hex number e.g. 0x2000
to decimal 8K
[STM32xxx] gcc_arm startup files

Updates startup files to actual versions of STM32 Cube drivers without
any changes of STs drivers:
- DISCO_F303VC
- DISCO_F334
- NUCLEO_F030
- NUCLEO_F072
- NUCLEO_F302
- NUCLEO_F334
[DISCO_F303] missing wrap main in gcc_arm template
Merge pull request #767 from ohagendorf/nucleo_disco_coide

STM32xxx: CoIDE/gcc_arm exporter and startup_stm32xx update