Fix CondDBBrowser runtime and drop Qt4

Propagated from 2018-patches (see MR !1241 (merged))

• cce24d06 Add runtime dependency on libxkbcommon.so
• 005a884b Reformatted CondDBBrowser code with yapf
• d2722bc9 Drop support for PyQt4 in CondDBBrowser
• 1e4147c1 Update "about" dialog

@clemenci FYI, I assume you want this also in master?

Yes.

• [2018-04-14 16:18] Validation started with lhcb-gaudi-head#1834
• [2018-04-15 00:10] Validation started with lhcb-clang-test#921
• [2018-04-15 00:10] Validation started with lhcb-gaudi-head-py3#124
• [2018-04-15 00:14] Validation started with lhcb-tdr-test#120
• [2018-04-15 00:14] Validation started with lhcb-head#1819
• [2018-04-15 00:14] Validation started with lhcb-gaudi-head#1835
• [2018-04-15 15:34] Validation started with lhcb-gaudi-merge#485
• [2018-04-15 16:22] Validation started with lhcb-gaudi-merge#486
• [2018-04-15 21:24] Validation started with lhcb-gaudi-merge#487
• [2018-04-16 00:09] Validation started with lhcb-clang-test#922
• [2018-04-16 00:10] Validation started with lhcb-head#1820
• [2018-04-16 00:11] Validation started with lhcb-tdr-test#121
• [2018-04-16 00:12] Validation started with lhcb-gaudi-head-py3#125
• [2018-04-16 00:13] Validation started with lhcb-gaudi-head#1836
• [2018-04-16 15:30] Validation started with lhcb-gaudi-merge#488
• [2018-04-16 16:12] Validation started with lhcb-gaudi-merge#489

merged

mentioned in commit 51752a50