[API] move SQLite into its own module

To break unneeded dependencies in postprocessing the SQLite part is
moved to its own module and namespace.
Therefore in the include and the function calls
"postprocessing" hast to be removed or replaced by "sqlite" e.g.:
#include "postprocessing/sqlite/SQLite.h" ->
#include "sqlite/SQLite.h"

postprocessing::store... -> sqlite::store...
34 jobs for 97-move-sqlite-from-postprocessing in 256 minutes and 58 seconds (queued for 11 minutes and 28 seconds)
Status Job ID Name Coverage
  Pretest
passed #290249
docker
clang_8.0_hybrid_dbg_sp

00:37:03

passed #290248
docker
gcc_9_hybrid

00:14:27

 
  Test
passed #290271
docker
clang-tidy

00:02:55

passed #290265
docker
clang_4.0_hybrid_dbg

00:15:42

passed #290266
docker
clang_8.0_hybrid

00:11:21

passed #290269
docker
clang_8.0_hybrid_dbg

00:16:09

passed #290268
docker
clang_8.0_mpionly_dbg

00:15:03

passed #290267
docker
clang_8.0_serial_dbg

00:31:34

passed #290270
docker
doc

00:03:05

passed #290258
docker cuda
gcc_5_hybrid_dbg

00:19:05

passed #290259
docker cuda
gcc_7_hybrid

00:14:21

passed #290260
docker cuda
gcc_7_serial_dbg

00:15:34

passed #290272
docker
gcc_8_hybrid_dbg_noboost

00:57:31

passed #290263
docker
gcc_9_hybrid_dbg

00:34:03

passed #290264
docker
gcc_9_hybrid_dbg_sp

00:34:03

passed #290262
docker
gcc_9_mpionly_dbg

01:01:27

passed #290261
docker
gcc_9_serial_dbg

00:58:17

passed #290250
intel docker
intel_17_hybrid_dbg

00:46:26

passed #290251
intel docker cuda
intel_18_hybrid

00:42:39

passed #290252
intel docker cuda
intel_18_serial_dbg

00:40:28

passed #290253
intel docker
intel_19_hybrid

00:51:30

passed #290256
intel docker
intel_19_hybrid_dbg

00:57:17

passed #290257
intel docker
intel_19_hybrid_dbg_sp

01:01:16

passed #290255
intel docker
intel_19_mpionly_dbg

01:40:43

passed #290254
intel docker
intel_19_serial_dbg

00:38:55

passed #290281
mac
mac_MpiOnly

01:13:29

passed #290280
mac
mac_MpiOnly_Dbg

02:00:55

passed #290279
mac
mac_Serial

01:24:03

passed #290278
mac
mac_Serial_Dbg

01:39:55

passed #290275
win
msvc-14.2_Hybrid

00:30:04

passed #290273
win
msvc-14.2_Hybrid_Dbg

00:43:13

passed #290274
win
msvc-14.2_Hybrid_SP_Dbg

00:42:22

passed #290277
win
msvc-14.2_MpiOnly_Dbg

00:39:28

passed #290276
win
msvc-14.2_Serial_Dbg

00:35:24