Several improvements: Support move semantic + remove vector in favour of std one + add support for std::string with -D DASH_USE_STL_STRING=1

[mathieucarbou]

Several improvements in this PR:

1) using std::vector instead of current vector class

2)Support for move semantic for strings to avoid a buffer copy for rvalues

Move semantic allows to avoid a second buffer copy when calling ESP-DASH with rvalues like that:

card.update(String("Hello") + " World!");
card.update(WiFI.localIP().toString());

The created buffer will directly be transferred to the internal class, which reduces heap fragmentation.

These update() calls being frequently called so this is a relevant optimizaiton.

3) add support for std::string with -D DASH_USE_STL_STRING=1

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[mathieucarbou]

I have read the CLA Document and I hereby sign the CLA

[mathieucarbou]

@ayushsharma82 : FYI.

I also have the same commits for the pro version in my dev branch.

I refreshed them just now (minor cleanups) and rebased.

[ayushsharma82]

Thanks @mathieucarbou , I'll merge everything in upcoming days.