Add units parser for the quota

[hardillb]

At the moment quota's are specified in bytes, this PR allows units to be used

It uses the xbytes package with the following suffixes:

Index	Prefix	Decimal Bits	Binary Bits (IEC)	Decimal Bytes	Binary Bytes (IEC)
0	-	b (Bits)	b (Bits)	b (Bits)	b (Bits)
0	-	B (Bytes)	B (Bytes)	B (Bytes)	B (Bytes)
1	K	Kb (KiloBits)	Kib (KiloBits)	KB (KiloBytes)	KiB (KibiBytes)
2	M	Mb (MegaBits)	Mib (MebiBits)	MB (MegaBytes)	MiB (MebiBytes)
3	G	Gb (GigaBits)	Gib (GibiBits)	GB (GigaBytes)	GiB (GibiBytes)
4	T	Tb (TeraBits)	Tib (TebiBits)	TB (TeraBytes)	TiB (TebiBytes)
5	P	Pb (PetaBits)	Pib (PebiBits)	PB (PetaBytes)	PiB (PebiBytes)
6	E	Eb (ExaBits)	Eib (ExbiBits)	EB (ExaBytes)	EiB (ExbiBytes)
7	Z	Zb (ZettaBits)	Zib (ZebiBits)	ZB (ZettaBytes)	ZiB (ZebiBytes)
8	Y	Yb (YottaBits)	Yib (YobiBits)	YB (YottaBytes)	YiB (YobiBytes)